Dealing with suicide of dad

HI, my girlfriend is 18. 12 months ago her father committed suicide. it was completely out of the blue and he left no note or reason. his girlfriend and step daughter blamed debt to be the reason. but nobody is completely sure. since his death it has come to light that he hung himself with a belt in my girlfriend's bedroom (she wasnt there) one night after an argument and the step daughter is now saying he sexually abused her for years. none of this is conclusive as its her word against a dead man.
my girlfriend suffered from anxiety attacks after his death and frequently has dreams about the actual hanging. these subsided a few months ago but she still has various episodes were she either loves him or misses him and hates him and is glad he's dead. i cant let her drink too much either as she goes into a blank state,wants to join him. im not saying shes suicidal because she's a happy girl but im wondering what i can do to help her, if there is even anythin you can do to help??