I would be nervous about this approach.
Yes, she should have to make a choice about how she learns because, ultimately, no one can force her to learn.
But teenagers can be very strong willed and can think that they are being forced into a particular choice when they're really not. Without knowing what Joe and his wife have tried, nor understanding more about their relationship with their daughter, I don't think that saying "Choose x, y, z or live elsewhere" is a productive strategy.
I assume she's under 18.
What will they do if she decides on the last option?
She may need to hit some sort of bottom before she accepts that she needs help. Confronting an impending reality may help. Teenagers often aren't rational though. Seeing beyond high school can be very, very difficult.
If she feels that her only choice is to leave, then it's possible (maybe even likely) that she'll not improve her math skills before more serious problems crop up.
Leaving home should never be a rash decision.
My $0.02.
Cheers,
Scott.
