The probe is just hanging free, and not measuring any heat pad temps?
340 grams is pretty darn low judging on my own records, which have my 3 snakes around that age between 500 and 700. I'm sure with proper feeding she'll catch up, but I wouldn't expect it to happen very quickly. I would think it would just take her a little longer to reach adult size than it would normally take, but I don't think her current size/age ratio will be any indicator on her overall adult size. Her spine does look a little too visible to me, but I wouldn't call her emaciated judging on your pictures.