I have learnt the hard way as well to never ever mix business with friends, at least not for very long. (I had taken in one of my friends daughter for 2 months at the last minute as she had landed a job before her daycare start, and that was great, but i let her know early on when she was debating about keeping her daughter here with me instead of the daycare that I really value our friendship and in this business something always comes up so I'd rather not do a longer term) and we are so both glad we did that!
Glad this ones not a super close friend to you. No matter how great they are or how great it seems, somethings always going to come up. I agree with Crayola Kiddies on this one. Mom is totally blowing things out of proportion. Of Course your child is going to get hurt here and there. That's what happens to kids. Especially in group care. I don't see this one ending very good. Would totally prepare to fill the spot and find a replacement and let them go. Especially cause she is on Matt leave, so not a big deal for her. If she thinks she can do a better job then let her do it. She's trying to grow a bubble wrap kid which is just impossible to maintain and achieve.