Is this common? how to deal with this?

[pucca]

I have dd who is 3yo and ds 6mth, dd adores ds, always playing with him, making him laugh etc but today i told her off for something trivial so she decided to slap ds (in his chair) across the head/face and it definately was on purpose.

I told her off of course and explained why she shouldnt have done it but admit i still feel by it.

Anyone any experience of this?

tia

normal
dd2 has bitten dd3 when she's been told off for something else

Yeh, I stood on my sisters head once. There is 18 months between us and mum said everything was going weel when I got up and stood on her head while she was getting her nappy changed.