I'm not sure I understand what "pop off her head" means. But it sounds like your child got a bump, the teacher applied ice immediately, and you got an incident report. This is so routine. If I understand you, the child fell but didn't cry, so obviously it wasn't a big deal. The teacher did see the bump later on and responded. The safety of all the kids IS her concern - she wrote a report and put ice on the child - and while she was doing that, she wasn't watching 7 other kids, right? So you have to have realistic expectations.
The ratio is 1:8. When my son was 3, the ratio here at home was 1:1. He fell, got bumps and bruises, cut himself, and routinely told me he didn't know what happened. Stuff happens. Our bodies are supremely well designed to heal up from bruises, cuts, and bumps. My son always had bruises from ankle to knee from clunking against the steps or running around - the pediatrician always called them "having fun" bruises. So if I couldn't prevent every bump when he was home with me, without chaining him to a chair, how in the world could he function in the world without an injury?
If you want to pull your child out, go ahead. But where are you going to find an environment that doesn't allow the possibility of any injury? How will your put the child in larger classes at age 5? How will your child go through life with zero experiences - will she never ride a bike, play a sport, go on a nature walk, learn to swim, go to the theater because there are flights of steps, play on a playground, carve a pumpkin, ride in a car? It is just not possible to be so hyper vigilant throughout our children's lives that no injury will ever occur.
Personally, I'd be thrilled that the teacher noticed a bump that the child didn't complain about, that you got a written report (so it's documented, which a conversation with you is not), that you have a 1:8 ratio, and that the teachers are interacting with all the children during dismissal instead of talking to each individual parent about every single bump that might have occurred.