Hello!!
I so know what you are going through.
I don't care about the hair - that's fine - it's all in good fun! I've know child care providers that die their hair red for Valentine's Day and Christmas....that's NOT the issue. This issue is her hickies.
That is NOT professional and it shows her morals as well. She will HAVE to lie to the kids who ask her about the bruises on her neck. That, in my opinion, is NOT acceptable.
The girl also needs to know that hickeys are bad - she's breaking the blood vessels and capalaries in her neck - VERY dangerous. But really - right now, beside the point - the day care should have sent her home and made her put on a turtle neck or makeup. If she chooses risky behavior outside of the day care - fine - but she doesn't bring it to the center. PERIOD.