My step-sister has drug problems!!! HELP! shes ruining my life?

long story but ii need the help...ok ...my step-sister is15 years old. shes on drugs BAD! she takes those lil tripple c's && huffs dust remover. shes on probation && is gonna go to JDRC. ok...her dad is my step-dad && he wants to help her but she dont live with him. Her mama wont believe anyone when they tell her shes on drugs. Even her own son. my step bro took my step sis to the dollar store && she stole almost 20 packs of those pills. he told on her but she wouldnt believe. she gets in trouble all the time && when she gets caught with drugs...her mom does nothing about it. && her dad cant send her off because she dont live with him && her mom wont let it happen. everytime ii see her with drugs ii tell on her bc ii dont want anything bad to happen to her. at all ii dont wanna see her go down like that. BUT bc ii tell on her she has turned everyone against me xcept for very few people. she wants to fight me now. she needs help. but we cant do anything about it && her mom wont bc ....