Poorly hen

I need some advice. I have a small bantam hen who is roughly a year old now. She’s recently dropped a lot of weight and not eating much she was wormed 4-6 weeks ago and still not eating much so carried out a poo count and it was clear. Don’t want to throw everything at her as this can make them worse. She’s not eating grit, she will eat but crop is pretty empty but it does fill and empty as normal as she’s being coming in on a night for some warmth. I recently lost another hen as my dog got hold of her and I am thinking it was the stress from losing her as she’s not been the same since. Any ideas ?

How can you tell she is not eating much, bantams are very light to pick up. If free ranging, they will eat a lot of grass as well as bugs and get grit from the ground.
Make sure any enclosure you have is dog proof. 
My dog has a high prey instinct, but never jumped the picket fence until we had rabbits in the garden.
My hen has a wired greenhouse for a run.