Can I tell my friend that she shouldn't be naked in front of the kids she's babysitting?
It's great that you are going to let her know that. How do you feel about your friend as a person?
I have a problem with her. When I'm drunk I'm going to punch her hard in the face
Though I understand your desire for violence, you shouldn't be punching her for that. Report her to the children's parents instead.
I'm going to punch her as hard as I can. I have no other solution.
You have a choice to take appropriate action, or an action that can get you into trouble. The best thing to do is to inform the parents of what she is doing.