Mother of Son's Friend Doesn't Want Contact; Dad is Ok with It. Stuck in Middle

Hello. My son's (13 y/o) best friend's divorced parents disagree on their friendship. Both boys are undergoing treatment for depression with different therapists. The therapists agree that their friendship is healthy and good for them to have support from someone who understands what the other is going through. Mom, however, disagrees and thinks my son is a "bad influence", tells me their friendship must end, and sends me nasty emails threatening a restraining order when they have played together outside of school. The boy's father however, has the opposite view, thinks their friendship is wonderful, thinks his ex-wife is selfish, and will drive his son over to my house for them to hang out. My questions are:

does she have any legal recourse against me?
can she get a restraining order against my son and my family?
what should I do?

Thank you.

Mother of Son's Friend Doesn't Want Contact; Dad is Ok with It. Stuck in Middle