It is confusing me when it is at the end of the sentence...
Amelia Earhart also flew nonstop across the Atlantic; the first woman to do so was (her, she).
I am thinking try the sentence with one word at a time to see which makes sense.. so I am thinking she?
This can be a tough one. But you got it right -- it's "she."
As a predicate nominative (following a linking verb), you must use the subject pronoun.
I startle some sales callers who ask if this is Sue. I answer, "Yes, this is she."