ok when I was 18 I got married (we had a kid together and he usto hit me when he drunk to much,,which was all the time..it started as just slaps,, then it got worsh,,, you allways think some how its your fault or that they are just drunk so they dont know better,,,BUT THEY DO. I only told my sister when he first started to do it but I would never tell them the bad stuff that went on.....I was lucky and got out of that ...you guys sound young,,and it sounds like there may be more going on then she even tells you.. if you want to be a good friend then dont keep you mouth shut..speak up..tell your mom. tell your teacher,, tell anyone close to you..thne they well make the call , and it well not be on you,, if thatw what you are afread of.. but doing nothing is being a bad friend,,,yes she may get mad at first, but she well get over it..trust me...and you well know she is safe...please be a good friend and tell some one...do it for her..