I wonder if in some way, at some level - perhaps not your rational mind - when she hurts you, you conflate her in your mind with him, and all your own traumatic responses are triggered?
In some way - you feel frightened of her and you forget that she is a very small three year old who might kick and scratch and bite but is very much smaller than you. Many toddlers do that sort of thing.
She becomes the Violent Person and you the Attacked Person in the encounter. Again, I say this "at some level" - I know that rationally you know this isn't true, but at some level it is retraumatising to you?
Could you try to practise a kind of mindfulness about it next time it happens - she is three, I am the adult, I am the big person, I am in control, SHE is the small one, the one not in control, if I choose I can kindly and firmly pick her up and carry her to a safe place to calm down.
I wonder if she could sense that you were in that kind of mindset and not scared of her aggression, that you feel you are plenty big enough for all her big aggressive feelings, it would contain it for her and help her manage it.
Children are aggressive and they do lash out.
Please ignore if not helpful! Just my thoughts.