I know its not easy trusting again in time if shes clean you will see a different behavior. It takes time.
Being clean isn't going to happen overnight its a lifetime of trying for some.
Thats why in AA they have one chips and some have many one day chips but at least they are trying. Being and staying clean can take years with times of using growing less and less. Everyone is different.
The thing is you can love the addict just not the addiction. Instead of wondering is she or isn't she clean learn ways of detaching and enabling.

I agree with katrinka, being clean doesnt happen over night.
Her behaviour will stay the same until she learns how to behave "normal" again. She will achieve this by attending meetings & working the 12 steps, it will also take alot of time for you to trust her again, that is up to her to gain your trust.

Katrinka and Loumc are right... stopping the use of DOC - does not change the behavior. It takes years. Unless she is truly working a 12 step program and/or see a therapist, her behavior will not change.
The brain has been chemically altered. And many in effect remain a dry-drunk. no booze - same behavior.
Whether or when you trust her is up to you. Just remember, you cannot control, cause or cure her behavior or her addiction - all we can control is ourselves.
Hugs.

When I meet someone and they tell me something, I have to accept what they say until they've shown differently. If I couldn't trust anyone when they sought me for counseling then I would not be worth my salt because first off, I have to believe in them and believe they want better. It is my goal to listen and not give any preconceived notions, although I might have, until they have proven otherwise. AND, if they should have a fall tomorrow, it doesn't have any bearing on what they told me yesterday. Perhaps they were clean yesterday but had their fall today, and together we can get through and hope for the best tomorrow. It's all about helping the other when they've stumbled just as we'd like a hand when we do. We all will stumble and would appreciate a friendly hand, not one given reluctantly. Be Blessed.

my sisters not in NA or any sobriety groups...she claims shes doing it on her own. which i really really doubt. she got arrested a month or so ago for possesion with intent to sell. she claims that she was only holding it on 'accident' and that she never had any plans to use it. Uh huh, cuz i look like gullible gus.
she skips out on her probation meetings for weeks, then goes and turns herself in to the cops claiming she wasnt hiding, because if she was she wouldn't turn herself in. and each and everytime they buy it and let her go!
her behavior hasnt really changed. when i see her she hasnt been high, however i see her alot less then i used to because it got to the point where i couldnt handle her.
i just dont think that she has changed, and i catch so much flak from the people around me for not putting all this blind faith in my sister. someone actually told me that if i dont stand behind her then im setting her up to fail, and when she gets busted high then she will blame me. she does almost every relapse...because i dont 'support' her.
i cant do it anymore, just believe what she says and give her all my faith.
i sure wish there was a book somewhere that told me when she was clean for certain!

Well, there isn't any book and there are no magic numbers to indicate when someone is clean, but there is something you can do. Let her go. You need to move and let her go. Yes, and I mean that. Just as my family let me go was the only way I could find my way back. My mother and I haven't spoken in 21 years but that doesn't mean I am not glad to be clean. It was a great sacrifice but definitely worth it.

What about testing her. Not sure if she would agree to it by you since you doubt her but then again if she is clean I would think she would say ok sis and do it to prove you wrong.
Just don't tell her your going to do it because they have to much stuff they can take to hide it now.
It may not be the best answer for you but short of that learning to trust is very hard but Actions speak louder then words with everyone but especially addicts!
Or walk away as Brotherroy said.sometimes it is easier then being so upset like you are all the time.

You will know when she's clean. She will change. If she truly is in recovery. Anyone can stop the drugs for a time, but if they do nothing else, at some point they will pick up again. There is nothing worse than a "dry" drunk. And believing her will not come over night. You will have to see it by her actions. So, let her go. Everyone has their own bottom. And you don't have to believe. I remember the last time my ex came home, the counselors told him that I would not believe in him over night. He'd have to prove he had changed with time. Unfortunately, he went back to using. But for a time, he was beginning to change. And every time he said he'd be home and he was, I began to believe again. Every Friday he came home and handed me a paycheck, I began to trust again. So, don't let this bother you. And no you are not causing her relapse. It's great to have family support, but if she is truly wanting recovery, your trust or not trust, will make no difference to her, she will want it more than life itself.

I have went through the same thing with my sister several times. A month is not long enough especially on her own. As you probably know addicts are good liars, and an addiction is for life. A person has to constantly work on sobriety for the rest of their lives to make it work. Without a plan in place, I don't see how even if she was "dry" at this point that she would avoid relapsing if she hasn't already.
Maybe if she wants back in your life it should be attending a meeting together such as AA so you can work through the twelve steps together ( bonding and healing), or to maybe get some family counseling for the two when you want to recreate that trust. Something that will benefit both of you not just her. You don't want a codependent relationship with your sister that causes you to put yourself last. Nothing about her addiction whether she is dry right now or not is your fault. Everything surrounding her addiction is out of everyones control, the only person you can control is yourself.
It is important to set up boundries in any relationship.