When and how to tell my kid I’m trans

My situation is, I began transitioning in early 2020, just after my daughter was born. She’s 5, and never known me as anything but Mom. She’s in school now and starting to be introduced to other people and their points of view. I feel I’m going to need to explain that mom is trans before much longer, especially if someone else tells her “that’s your dad” (I pass fairly well but there are days where I’m not making an effort for the drop off line at school.)

So, like, when is a good time to introduce her to the concept? And how do I explain it within her simplistic concept of gender? And how do I do that in a way that won’t risk our safety or create problems for HER socially? What happens the first time she says “my mom’s trans?”

I’ve just got so much anxiety about this.