Hi Nene,
Welcome! Your caring and support will be valuable to your neice, but there is not really too much you can do unless she says she wants help. It takes a lot of motivation to fight an addiction and unfortunately it's not usually something that can be achieved without really wanting to be clean/sober.
If you like, also check out the NarAnon forum on this board which is for families and friends of drug addicts and you'll find others there, who are in similar situations to yours. Good luck.
Anna