it depends on what you mean by feminist. If you mean that a feminist is someone who fights for her God-given rights, then that is fine. God has given her those rights. Others are denying her and her gender those rights, and she is fighting to right this wrong. That is perfectly fine.
THe problem arises when feminists try to change the laws of God to fit their perception of the world. For example, feminists saying men and women should pray side by side, that women should lead prayers, etc. These things are not sactioned by the Quran, nor did they happen in the Prophets time, so anyone who tries to bring this into being is committing bid'ah, and that is where the problem lies.
However, a woman who fights for women to be protected, to get their Quranically-ordained share of inheritence, and who fight against domestic abuse, and not only doing right, but will be rewarded for encouraging the enforcement of Allah's laws and promoting justice.
Although we all like to believe that men and women are equal, it is true in terms of respecting them equally, but not in terms of roles that they play and actions they perform. If men and women were truly equal, the olympics, and all other sporting events would not have men-only and women-only events. Rather, men and women would compete shoulder to shoulder in them. However, since men and naturally stronger than women, this would mean there would never be a female winner of a physical sport, so equality goes out of the window in such cases.