In my experience with my kids and in a college classroom, the student isn't ready for a class if she forgets what she's been taught/needs too many reminders, and has to have her hand held in order to get through most problems (even on review). Another sign that a student isn't ready for something is the need for too much background information. If someone has to spend a lot of time explaining points A, B, and C so that the student can finally understand what a paragraph, lesson, or problem is about, that's not good.
AP science classes are designed around the idea that students already know a lot of basic ideas. They also move very quickly, which doesn't give a newbie much time to catch up, much less internalize ideas. So it very well be too much for someone who hasn't taken chemistry before.
Honestly, my kids have been in this situation once or twice, and we let them drop the classes. If your daughter is miserable, what's the point? She's only 11, so she has plenty of time ahead of her.
Last edited by Val; 11/14/14 10:47 AM. Reason: Too many typos