What to do about mean people?

my boyfriends 17 yrold little sister lashed out at me 2 nites ago. she yelled at me while she was already arguing w/ her dad. i was in the wrong place at the wrong time, but she said some very mean things to me and i stood up for myself. i have known the family for 2 years and she has blown up like this many times before but never directly attacked me (only indirectly like saying things that are mean about me to other people). problem is she never seems to take blame, and people will act like nothing happened the next day which i am not so good at. i feel like i dont want to be around her for awhile. i am not sure how long to wait to go over to his house but at this point i dont feel comfortable or welcome. my bf and i are starting to bicker about things despite him understanding my unwillingness to go over to his house. he has stood up for me but he still his frustrated about the situation. i just feel so icky about going over there and being around her & her moody self. Suggestions?