My cousin is homeless, but told me not to tell anyone?

About a month ago I found out my great Uncle's daughter is homeless. She is addicted to drugs and was put out of the house. I was walking home with some of my friends about a month ago and saw her with some other person sitting up against a building here in NYC with a sign asking for food..not money. I debated stopping but I did. I talked to her and bought both her and her friend something to eat and drink. She was very open with me about her addiction and her being kicked out. I knew this before but I always thought she went to Boston to stay with our other Uncle. That was over 3 months ago knew she left his house in Boston but no-one knew she came back to New York. She said she hasn't spoken to anyone in the family in two months. I'm the first one. She's 23 and I'm 14 and we kinda grew up together and were close before she got into drugs. I know her parents have tried getting ahold of her and stuff and even reported her missing. The Boston police wouldnt do anything because she's an addict. They said she as an adult and could leave if she wanted. I know her parents are super worried about her but she BEGGED me not to say anything about me seeing her. She made me swear I wouldn't. I've seen her a few more times since then and she still makes me swear not to tell. But its getting harder and harder to keep her secret. I know how worried everyone is and its really taking toll on my aunt and uncle. I want to tell my mother so maybe she could try to talk to her. Should I?