Hi and welcome, sorry about your situation.
Are you absolutely sure that she has been sober? I guess she might just be a person that needs a lot of alone time when stressed, however, taking off for days seems unusual unless there is something going on like drinking or some other mental challenges?
What your describing is not normal behavior, but i'm sure you already know that. You mentioning how different she is now from the person you met just might indicate that she was actually still drinking but of course that just a guess.