1) Casual attempt to compel Max might not work, given her crazy genetics and being not-quite-human. Rebekah having to put a lot of focus into the compelling once she realizes just trying to wammy her will work for a while.

2) I don't have a problem with the idea of Rebekah feeding off Max, however Max's blood is super-charged and highly regenerative and Rebekah may find it extra super nummy delicious. If Rebekah wouldn't have the willpower to stop, I'd definitely don't want Max to be drained or vampirized. I don't mind her being brought to the bring, though!