Although the sleeping a lot, does sound inconsistent with meth, your gut is telling you she's using "something". Though not always, the guts of addict's mom's are usually pretty accurate.
As a recovering addict, I totally agree with miss Done. I became an A (addict) in SPITE of the way I was raised, not BECAUSE of it. I know some A's will blame anyone or anything for their using. It's BS...it's just the A's way of denying responsibility for thier own actions.
Let go of the guilt..it's not yours to carry. Focus on you, and let your AD face the consequences of using. That's what got most of us into recovery.
Hugs and prayers!
Amy