I hate my sister....... i think she on drugs n stuff?

my siser ill call Nia is a slut.... she sell herself for and she has 2 kids already and she is only 18 years old....she drinks and stuff and bring strange men to our ome.... she already had several stds and started smokin weed recently... countless times she swore she was gonna stop but she keep selling her self. well last week she was d and fears she may be pregnant..... she came crying to me to help her pleading, she said she didnt want to live that way no more..... i never saw her like this before but im tired of her going bac to prostituting and striping...... do i beleave her and help or do i leave her alone because i cant trust her no more. i really need yall help... parents wont do because my dad died of cancer when i was 12 and mom is in jail due to drug charges.... me on the other hand is an honor student and i play basket ball.. im 17 and has 2 jobs to keep our apartment