Need Advise - My Sister's An Addict

How do you know if a recovering addict is using again? I don't want to jump to conclusions but I also don't want to be naive and believe that there's no possibility of relapse. My sister has been going to meetings every day (at least what she's telling me) and seemed to be doing very well. Her attitude was positive, she was happy & outgoing & involved with the family & everything that was going on. Since this past weekend, however, she has been reserved & more absent than present in the family. She's been sleeping a lot & claiming that she's not feeling well (vomiting & diarrhea). I truly hope this is some stomache flu but how long do I believe it's a virus vs. the disease of addiction & how do I go about finding out without alienating her from me? The last thing I want to do is be an enabler, either by ignoring the possibility of a problem or by making it OK. I would appreciate any advise. Thanks.
well if shes using again she will show lots of signs like the 2 you wrote are her eyes pinned up ( really small)? her attitude is bad easy to anger,sweating cant sit still or if sitting still falling asleep,itching,digging,try asking her and if she flipps out or acts guilty she probably is .i just went through this a week ago so im very sure that these are some of the signs good luck and God bless
One of the ways I was truly able to determine the drug use was follow the money. Tell her of a budgeting plan where you to will save reciepts of all money spent for a few months to see where you can start saving money. When I did that of course he tried but then all of a sudden he would say he bought things off the street that cost so much and that they don't give reciepts. Or he bet on a football game and lost, he didn't even like football. But then I found the pattern 20 dollars on the first and 60 dollars every 4-5 days later it became real easy. The money tells all. But the physical appearance and attitude reveals the same also. Vomitting was a good sign for me.

Offer to go to the mettings with her. Oh I also set up a camcorder when I wasn't home to catch him talking about whatever might give me clue, that never revealed anything he was very careful.

God Bless you I will pray for you and your family it is never easy but you must stand firm in your decision to help her and enabling will only hurt her. Keep that in mind.
Thanks to you both for responding & for the good advice. I will be keeping my eyes & ears open so that I'm not blind to what is going on with her so that I'm able to help. She's a good person & I know this is hard on her. Thanks for the good wishes & I will also keep you both in my prayers as well.
I also had to differentiate between the personI knew and the addict he once described himself as a "barrell of contradictions" Remeber to be a successfulll addict you must be a better liar. So I say this to you only for you to see that the person you knew and love is not the person that is in front of you. For the addict has only one true love so proceed with caution and love, but do not go blinded by words.

Keep in mind a tree is known by the fruit it bears.

God bless and keep in touch.
if it is really bad you should tell her she has 2 get help and fast.