I need desperate help please?

im bec 13 and my cuz heather is 14 in may she tried to commite suicide two girls put tampons in her locker b/c she hasent had her period yet and they made up jokes sayin she was fat (she ways 71 Lbs cuz she was anarexic) heather is now becoming friends with the two girls and i told her i woldnt tak to her unless she unbecame friends with them is this a good desicion?