I was able to find some fish antibiotics that can be shipped to the UK for just an extra fifteen pounds. Not Baytril (Enrofloxacin), but I was able to find Ciprofloxacin which is of the same family class as Baytril and has good coverage against coliforms such as E. Coli which is often found in EYP infections. Here is the link if you care to take a look :
https://www.entirelypets.com/ciprof...0367&cjevent=0cda5dba192411eb80e3006d0a24060c
Regarding her crop, in the morning it should be empty, not full, so the fact that you felt it and it was full suggest there is crop statis going on. Is this being caused by the EYP, possibly, every time I've dealt with crop issues, specifically sour crop, it's been due to infection/ reproductive problems. Personally, if she was mine, I would consider euthanizing since she's not eating, or drinking, shes producing yolk-colored droppings, and the crop isn't moving properly.
You could try treating her, but I'm afraid her system is failing regardless, and while you may be able to keep her alive longer, she's going to pass.
Eggcessive, and Wyorp, have more experience with this than me, so I would wait for their opinion before doing anything.