Aww, I'm sorry to hear that.

I wonder if she just resents having to do more school after school. Maybe if she were homeschooling and had more free time AoPS itself would be okay? Just a though, I know the time commitment is pretty high with that program.
We seem to get math frustrations both if the math is too hard and if it's too easy. It drives me crazy

and my DS is only 6. It can't be perfectly matched all the time, so they need to be able to deal with one of the two I guess.
Not sure it would work but could she take a step down in difficulty level? If she wasn't too bored and still kept fresh on things, it might be okay. Maybe she can do ti but doesn't want to excel in that area, so it's hard to push that hard...
Or maybe the math program isn't a good fit, too... just thinking out loud.
Good luck!