SoberRecovery : Alcoholism Drug Addiction Help and Information

Just found out yesterday that my sister, who I thought has been clean of heroin for 2+ plus years, is using again (still?).
Her friend told me he didn't like what he saw, how she's lying to me and the rest of the family, and using us, as well as taking money from Dad's business ('skimming off the top' I guess you'd call it). She gave him money to get her some bags when we worked yesterday; he is not comfortable doing that for her, and says he won't do it anymore. (He's related to her incarcerated boyfriend, and I guess he was trying to take care of her.)
I have been her main champion, sending her monthly congrats on her clean-anniversary, driving her places, helping out with food and money, defending her when her own kids have talked S**t about her, et cetera.
Now I feel stupid, foolish, betrayed, like I've only been enabling her, that she must feel she 'got one over on' me, and so forth. I am now re-thinking recent times when money's gone missing around me, Mom, and our aunt, especially after her friend described how (slickly) she took money when making sales at work. I think I have to make sure that both of them change their debit card PINs, and not let her do their shopping (which of course makes more work for me, if we can't trust her to do it)
Oh, too much to think about! I have not yet let her know that I have this new awareness, nor have I told anyone else what I've learned yet, either. :gaah