Its really up to you if you want to remain friends or not.

The thing is that he is her son not yours and she can raise him how she wants(Without abuse of course). I mean everyone raises their children how they want them to be raised. I hoestly don't think its anyones business how I raise my children....you get my drift.......LOL Its really your decision if you can sit and watch her smack her son when it clearly upsets you.......Each to their own.