Lab,
I'm sorry you are having to go through this. It is such a helpless feeling to suspect, be told, but still have no concrete info on such a serious issue. You've come to a good place for support and information.
A couple of thoughts came to my mind in reading your post, first, you said you haven't found any meds...but you stated that she pops ambien like chicklets....ambien, to my understanding is an addictive drug (someone please correct me if I'm wrong). The other thing that popped into my mind reading your post is that regardless whether you find that there is an actual 'drug' problem or not...there 'some' problem. Things are not okay when you are working 2 jobs, paying her end of things, keeping your finances seperate....maybe don't stress yourself in having to 'diagnose' the right cause. That doesn't have to be your job, you just need to identify the things that you see, feel, experience, that are not within the realm of healthy boundaries. You are not superhuman...take one step at a time, deal with the things you know and be open to learn more as you go along.
Frog_2Hop