Fist fight ??

I got into a verbal altercation with my SIL and it escalated into a fist fight. She's been spreading rumors about me that are completly untrue and filled with outlandish accusations so I confronted her about them. She started saying 'You're lucky you're even with my brother or I'd beat your ass.' To witch I responded 'Why does that matter?'. Looking back I can see how someone might take that the wrong way but I didn't mean we should fight anyways but that's how she took it. She grabbed my hair and it was on from there. Now I don't know if I should go to his mother's house for Thanksgiving or sit this one out.. What would you do?,