Tsk Tsk Tsk naughty naughty human....

Youve trained your pup not to bark and not to respond with force yet thats exactly what you did....

First thing with any change of behaviour is to check that there is no medical issue. So a call at the vets should be your first port of call...

 

My guess would be that it's just a little loss of control with the excitement of playing. Maybe restrict that type of play to outside but if she continues to do it, get her checked by a vet.

But scolding her and punishing her isn't the way to address it. In fact, scolding a dog for indoor accidents can make them think they are being scolded for toileting and not for toileting indoors, so they seek or create opportunities to toilet when you are not there. Then you find the result much later. Not what you want.

So hard as it is, try not to react.

Edited to add - cross posted with @Mad Murphy

 

Please do not punish your dog like that, and especially do not ever slap her. that is very unfair to her and also counter-productive.
If she peed on the rug it may have been from a medical issue so take her to the vet. that should be your very first reaction, not hitting her.
Now that you have scolded her and slapped her while playing with her she may be associating the scolding and slapping with the play and is now afraid or nervous to play and that is making it even more likely that she will pee in the middle of it, assuming it is not a medical issue.
But if this is a urinary tract infection, she needs to see a vet right away before it gets worse.

If she checks out OK at the vet, don't ever punish or slap her again like that.
I would suggest playing with her outside, so if she does get overexcited or nervous she will pee outside....no problem. When or if she does, ignore it.
If you do that for a couple of weeks and don't play the game with her inside, it may let her feel comfortable with the game again and you will not have the problem.