sorry to hear poppy is unwell again,hope the vet visit gives you some insight/advice to help.
regards to using blow dryer, the way I dealt with leo (and our gsd before him), was to offer one treat for sitting down, then if you need to tie them up so they can't ran away (if you need too, didnt have to with leo hes dopily wonderful lol) let them smell the hair dryer, then switch it on low away from them so they can hear it, turned it off so they can smell it again, then switch it on and dry them, then after its done they get another treat.
I think offering treats when they aren't settled isn't a good idea. (but I dont know if poppy was settled or not)
but I do hope her tummy upset is just fromt the treats and not an underlaying issue.
Good luck at vets