It's always hard to give others advice regarding their own family situations and I can truly understand how torn you are. I have, however, been through the same with my sister. I felt, after years of thinking I could help her myself, that putting her in the hands of the authorities and letting her get a taste of the real consequences of her actions was the best course in the long run. Being an "enabler", no matter how much you love someone, does not help them in the long run.