I'm surely not alone in thinking of birth marks as something completely normal and natural and very silly for anybody to judge.
My husband has a birth mark like the one you described your dd to have and in the same spot, I've never judged him for it and he doesn't think anything of it either. To me a birth mark is like a beauty spot or freckles. It's there and not everyone has it but it's completely normal and nothing wrong with it.
I personally wouldn't even bother removing a birth mark on my child if it was visible to others and lasted into their older years. It's how they were born and if anyone judges them for how they were born then that's their problem not mine.