How do I help my older sister?

a year ago my dad died in acar crash...my sister has blamed her self ever since. shes so cool but she gets on these highs and is kind of obbsessive shes always been like that but my dad was the only one who could contorl her. she used to be so close to him and took it the hardest when he died. so she gets on emotional highs and then hits rock bottoms, for days sometimes and my dad used to be the onyl one who could get into her during that time. then the same time as my dad died her dumb-@ss boyfirend cheated on her and made her feel like crap. she nevr got over either thing. well anyways tonite is one of those nites shes on a real low and it always scares us because we dont know what to do sometimes we think shes really going to do something horrible its like she closes up and is in her room for dayz- today she got back from soccer pracite and went to bestbuy with her friends and then suddenly she got back and was like so sad and she just piut on her pjs and went into her room and has been inthere ever since. she used to snowboard and sing and be so lovely now shes like a huge flirt, she lets guys just use her and idont know why she never did that before. shes went so crazy like shes scared to let us see her please help! what can I do??

Sorry for the loss and you can tell her that she will find another boyfriend out there who is better and try to talk to her when you are by her door she should be able to hear you, but you need to try to talk to her somewhere and just say that it is not her fault and give her comforting words to make her feel better and try to help her stop changing so much and she will still be sad that her dad is gone, but she will also start to understand to not cry as much as she used to because it was not her fault.