Do you think I should ask my girlfriend to stop being so violent whenever she complains about her problematic sister-in-law?
How does your girlfriend express herself violently?
Because she always kicks me in a way that leaves a bruise.
Your girlfriend's anger and abuse issues could stem from some emotional issues she's trying to deal with. Try to get her some help and see if she can work through her problems.
Dude, I have a bruise where I was kicked on my leg. She needs to get rid of that bad influence in her life and apologized to me.
You should go tell her this then, because I agree with you! You should always speak up when you're met with violence by a loved one.