Hi Megan,
As a general rule, prior to 1890, you are more likely to identify passengers at the port of arrival as opposed to the port of departure. You need to check the website of the appropriate National Archives, in this case, the
National Archives and Records Administration in the USA.
Prior to 1864 records were kept in the form of church and parish records, while some of these have been regrettably lost, all the surviving records have been sorted into
county-based genealogical centers. This link also includes property and landed estates, so this could help with your research on Margaret. You can also search the church records
here.
Let me know if you have any other questions and I will try to assist.
Cathaoir