Well, now, let's not get carried away! She knows of his issues. Not sure she actually likes him!
LOL In fact, at this point I am not sure how she will react when she sees he signed up. She could be discouraging if she sees him as a pita. He was in her pull-out not because of her but because he passed a test every month.
If she understands him well enough to be an ally and advocate at IEP meetings that is pretty good. If you feel she gets your kid in a way other teachers don't, that may be as good as it gets.
If you are concerned, I would ask her what she thinks.