I'd stick with a good meal every 7 days and just slowly build her back up plus using that Provent-A-Mite. You don't need those nasty things back again. Also I'd really suggest a fecal float done when she next passes feces. It's not overly expensive and with her poor care in the past and being infested with mites and all that, well a fecal would be my next step to rule out any other issues with her weight. Of course a good going over by an experienced herp vet is never a bad thing. If she came from a breeder, did she come with the mites or did they get into the collection through another snake?

Quarantine is your safest bet when it comes to adding snakes to any collection.