I don't do end of year gifts. This year I did have pang of guilt about that because DD1's teacher was AWESOME, but I've got more important things to deal with, and I'm broke this time of year. I always give token gifts before the Holidays (lately it's gift cards) and have the kids write/sign a quick note - even if I HATE the teacher. But every year is different.
If the teacher was that horrible, I would not spend another second worrying about it, and just don't do it.
Depending on your personality, school situation, community ramifications, etc, I would consider writing a "thank you" in appreciation of her making a bad situation worse. Even if you tear it up, it might make you feel better.