First time cat owner. Timid kitten lost confidence after rough play with other kitten.

Just adopted two kittens (3mo female and 5mo male) five days ago. Boy is super confident. Girl was timid to begin with but gaining confidence as time went on. When they would interact, the little girl would hiss and bat at the boy but would follow him where he went, run at him, hiss, run back, then run at him again.

This morning the boy grabbed a hold a wrestled her which maybe was a bit rough for her. She's now stopped following him around and when he approaches her and tries to engage play she hisses and growls but now with her ears flat and will move away. He will flop down in front of her and still she will move away. Also with her interactive play, she seems a lot more restrained and will sit next to a shoe or something and swat and the toy from there but won't run after it like before.

She's super cuddly with me though and isn't as flighty as when we first got her. The change is just directed toward the 5mo old. He is also a bit bigger than her.

Is this a passing thing? Should I do anything different? I've just been playing with them with separate wands in each hand and feeding them with their bowls side by side. She will come up and eat next to him but will growl if he sticks his head too close.

I don't know, because I want them to be best buddies but it seems she has taken a step back confidence-wise. Any advice would be appreciated.