Interesting! I got the opposite impression from the trailers. For instance, in the book, did she ever have sword-play with Aragorn and beat him (not that physical might equals feminist)? I don't remember that, although it was a year ago that I re-read the book. My impression of the book-Eowyn was that she was the queen of unrequited love (re: Aragorn). She did go to war in the face of opposition from her family, which I agree is a strong woman thing to do - but why did she do it? I wouldn't necessarily project feminist motivations on her.
Which, of course, is not necessarily *bad*, it just means that I don't necessarily believe she was a strong feminist. I think she was a tragic character, someone who was unrecognized by the people around her for her strengths. I can't remember, does Theoden even realize that it's she who saves him?
I think it's a really strong comment on the non-feminist tendencies of the book that someone so strong in swordplay and battle would be left at home while all of the other (male) people who were renowned for the same skills went to war. However, I don't knock it - it wasn't written in current times, after all.
What did you think was so feminist about her character?