Friend taking advantage.

[SillyGirl_C]

Tough spot to be in. I deal with difficult people all the time and the best way to talk is face to face. Phone or email tends to escalate situations.
I would meet with her and tell her straight up that you have been dreading this conversation. Although you want to help her out with before and after care, you technically don't have the space and you have a waiting list. Tell her that although you prefer her munchkin, showing preference damages your client relations and reputation and it is a small industry. Before not a problem as it was emergency only...but now you are over numbers consistently and at risk of a major issue.

Offer to help her until the end of October if she is in a jam.
If she still takes advantage past Oct 31st or acts like a total ass when you are bearing your troubles, she is not a friend, just another person with an over inflated sense of entitlement.