I had been told that she was a first cousin to Rose Fitzgerald Kennedy; when I found a Mary E. Fitzgerald, born in 1883 who was the daughter of James Thomas Fitzgerald (a brother of Rose's father John Francis "Honey Fitz" Fitzgerald) I thought I had confirmed this.
I was a cousin of the Kennedys! Never mind that I can't stand this family, I had famous relatives that I don't have to go back 7 or 8 generations to get to.
Well... not so much.
You see, the Mary E. Fitzgerald who was the daughter of James Thomas Fitzgerald was not my great-grandmother. I came across a marriage record, courtesy of FamilySearch.org, of James T.'s daughter to someone not my great-grandfather. I then found, at the same source, another marriage record there for my great-grandmother Mary Elizabeth's marriage to my great-grandfather, and her parents are listed there as being Thomas FITZGERALD and Rose KILEY*. Her death certificate also gives the same names for her parents.
Thus far I can find nothing else on Thomas and Rose (Kiley) Fitzgerald.
Mary Elizabeth may well be somehow a cousin of the Kennedy Fitzgerald family, but if she is, it's through some other connection.
* Update: the name "Kiley" is actually "Connelly"
Thomas FITZGERALD m. Rose CONNELLY
Mary Elizabeth FITZGERALD (1879-1954) m. David Thomas RYAN
Clare Regina RYAN (1911-2001) m. Bernard KRANTZBERG
My father (living) m. S. HOWES
Me (b. 1974)