This will be a multi-part answer because I am still not certain exactly what the question is asking. Since the original question suggests that the research subject may have come to the USA, I'll assume for the moment that the passenger in question came here.
- Q: How can I find someone's arrival and entry into the USA?
The first rule of genealogy is "start with what you know". When working a problem, it helps to generate a list of all sources consulted, and to assemble a biographical sketch that includes all the information contained in those sources, with a notation of where the information comes from. Locating the research subject in time and place allows the researchers to narrow down the window of opportunity for the voyage to take place.
Example from my own research: my husband's family came to the USA, stayed a few years, and went back home -- and some of them came back to the US later on. Family records gave us the dates of entry into the USA, but I did not know the date they returned to England. By collecting records about the family in the USA, I was able to deduce what year they returned to England, a deduction which was confirmed when I found one of the later manifests which stated when the family member had been in the US before.
The page Sources of Genealogical Information lists the following historical records as possible sources of immigration events:
Alien Registration, Citizenship Papers, Crew Lists, Customs Records,
Deportation, Immigration Aid Societies, Letter Books, Log Books,
Naturalization, Passenger Lists, Passports, Protocols, Register of
Seamen, Vaccinations, Visas
Even if you have a year of immigration from one of these sources, it is useful to find other evidence about your research subject that will support or contradict this time frame. You will need the information in this supporting material to make sure you are looking at the records for the right person, and not someone else with the same or similar name. The FamilySearch Wiki's article How to Recognize your United States Ancestor has tips on how to make a timeline and make a biographical sketch. The number of questions found on the passenger lists changed over the years; The Capital Area Genealogical Society has links to ships passenger lists excerpt forms which will show the questions asked for different time periods.
- Q: How can I locate passenger manifests?
It is a common misconception that all immigration into the USA came through Ellis Island. The reality is that there were many different ports of entry into the US, and if you assume your research subject came through Ellis Island and don't check the other ports, you may miss finding their actual arrivals. (Note too that people sometimes traveled back and forth multiple times, so the same person may have more than one transit and thus more than one passenger manifest. Their arrivals might be at different ports, as was the case for my husband's family.)
Finally, once you locate a manifest, you have an important question to consider:
- Q: Have I found the right person?
The FamilySearch Wiki's article How to Recognize your United States Ancestor has tips on how to make a timeline and make a biographical sketch. The number of questions found on the passenger lists changed over the years; The Capital Area Genealogical Society has links to ships passenger lists extract forms which will show the questions asked for different time periods. It can be useful to look at a blank form and make a list of the answers you expect to find on the manifest for the person you are seeking, but bear in mind that not all the answers you may find will be 100% accurate. With a few exceptions (e.g. the Records of passengers held for special inquiry), US passenger manifests were filled out at the port of departure, and your research subject may not have provided the answers to the questions (e.g. if someone else bought the ticket for her). It is treacherous to try and match someone by name and birth date alone -- ages are notoriously inaccurate on the manifests. If you are working from a transcribed index, be aware that indexes may not be accurate. Volunteers do the best they can, but it is not always easy to read the handwriting of the people who filled out the original forms, especially since the volunteers often work from digital images, rather than original records, and the images are in black and white, which are harder to decipher than color images, which are better at showing differences in inks or pencil.
Example: searching for my husband's grandfather's first entry to the USA by his name will fail. Ancestry.com's index shows a completely different reading for the surname. He does not appear in the manifest under his own first or middle name; the manifest shows a child of about the right age but with his father's middle name (which is also the name of one of his cousins). The rest of the family is a match, and the month, year, and ship name matches with information I had from the family records. The birthplace information and the contact information for the relatives/friends in the USA also matches information known from other sources, so despite the fact that most of the ages in the manifest also do not match the expected values, I am confident that the manifest is the correct one.
So where did the confusion come from? The question about who purchased the ticket shows that the tickets were bought by a relative (the sister of the head of household for the family on the manifest). An aunt is more likely to get the name of a child wrong than the child's own parent. (It's also important to recognize that the handwritten biographical sketch that came down through the family was created at least thirty years after his first arrival into the US, and at least twenty years after his second arrival; it is likely that this summary was written by my husband's grandmother, who was not a witness to the events.)
If your question is, literally, How can I locate her on a passenger manifest? -- because you have an arrival, but cannot find her by name, as in my wrong-name case above, then the brute-force way would be to go to Steve Morse's website, use one of his search forms to enter the name of the ship and the arrival date, and to page through the images as if you were reading the microfilm in a library. In that case, it may be especially helpful to familiarize yourself with the nature of the records first. See the following articles for more details about passenger lists and about the immigration and naturalization process:
If by "departure manifest" they mean the outward passenger lists created in the UK by the Board of Trade, those are held by the National Archives at Kew. See their page on emigration:
Outward passenger lists in BT 27 (1890-1960) contain the names of
people leaving the United Kingdom from ports in England, Wales,
Scotland and Ireland for final destinations outside Europe and the
Mediterranean Sea. Some BT 27 records are available to download from
findmypast.co.uk. Registers of passenger lists, 1906 to 1951, are in
In my experience, if you know that your passenger did travel to the USA, it is much easier to identify the right passenger by searching the more detailed USA records first. After you know the that you have the right person, and you have found the right manifest from the US records, you can enter the ship name and date of departure (which will be on the header of the manifest) to search for the corresponding UK departure list on FindMyPast. However, the Ellis Island records and records from other ports in the USA won't help you if the person went to Canada or some other country. This is why the biographical profile and information from other historical records are essential when you are trying to find passenger manifests.
I can't emphasize enough the value of simply writing down a list of everything you think you know, and where you got the information. In the process of doing that, it is easy to discover that you actually know more than you thought you did, and to find other questions that you can answer, which provide more clues to find the manifest you want, or to recognize the right record when you have found it.
Since your purpose in finding the manifest is to provide proof of her emigration for a permanent monument, it may be appropriate to hire a professional genealogist who is already familiar with immigration records from that period. A professional will already know what records were created, what records survive, who holds the records, and what other records (like Naturalization records) hold clues that will help locate a manifest.
If there are too many discrepancies between the manifest and the other records you have about your research subject, the agency in charge of the memorial may want a proof statement showing why the records do not match, and a professional should be able to take care of that for you. If you do hire a professional, he or she will need the same kind of biographical information that is discussed in the articles linked to above.