Our little 8 month old pup was in the garden yesterday afternoon. When she came in she was panting hard, although she hadn't been running around and was sitting in the shade.  The panting soon stopped but she started dribbling excessively and was clearly not right. I took her to the vet last night who suspected a bee sting and gave her a cortisone anti histamine jab.  He though she would be fine after a couple of hours.
Well today she is listless and not interested in anything, wouldn't eat her normal food or drink anything. So I cooked her a little minced chicken, which she has eaten and promptly brought back up. I think from her moving around that she has stomach pains.

Should I take her back to the vet or is this a normal pattern of behaviour for a dog that may have been stung ? Would a bee if swallowed cause stomach aches ? Thanks for any advice,

As your vet thought she would be fine after a couple of hours I would be inclined to give them a ring and see if they consider it necessary to assess her again or just let her rest.

Sounds like she may have eaten something from the garden?
I would take her to the vet again

yep, take her back to the vet, you can never be to careful.