Sister disappeared in New York City, what are my options ?

I come to this subreddit as I am desperate for help, I apologize if that is not the proper place. My sister has been living in NYC for almost 10 years now, she is french but got a green card. Almost two years ago she had some kind of burn out/mental breakdown and lost her job and all her friends. My mother and I finally convinced her to come back home, and last time we spoke to her she was supposed to leave her flat and buy a one-way plane ticket.

My mum speaks to her almost daily, but it’s been 3 weeks now without a single word from her. Now to be honest she already disappeared for a few months last year, so it could very well be her having another mental health crisis. But we have absolutely zero contact in NYC, all the people we knew moved out of the city. I tried calling her precinct but they tell me they will only do something if the request comes from an American citizen or if we are physically here.

We simply have her address and that’s it. What can we do to at least check if she’s home or not ?

Thank you for your help.

Update : she is definitely home. Even though she doesn’t answer the door, some really helpful people managed to get there and speak to her landlord, which confirmed with videos that she’s in the appartement. Obviously I resent her a lot for putting us through this, but at this point the only option is to go there with my mother. Not sure how we’re going to bring her back to France but we’ll see. Thanks a lot for all the kind messages and helpful tips, you’re a wonderful community.