I'm usually not one to sweep stuff under the rug, but in this situation I might just do that.
I would see it as the responsibility of a close friend to be able to be direct with both positive and negative feedback.
In other words, I feel my good friends should be able to call me out when I pull sh*t, and they understand I'll be more than happy to do the same with them.
Since she is not a close friend, I don't see any win/win situation in addressing her alcoholism and dishonesty.
I especially don't think it would be helpful to address issues behind her back to her roommate.
Next time you need help with the cats, line up someone else to help. If she ends up asking why(she probably has an idea why already)I'd just brush it off as. "oh we didnt want to bother you" etc.
I'd continue to be cordial to her as she obviously has a problem.
It's hard enough for close family and friends to address alcoholism issues with ones they love,
to help a casual neighbor friend seems like an even more daunting task.
Chalk it up as a learning experience ,and be happy larger items/ more precious items to you weren't ruined or stolen.
Just my take.