Droopy hen with small lump in neck

Hello everyone, just joined Hoping someone can offer some input on my beloved bird.. she is 2 years old, a rescue, and has stopped laying recently. She has lost weight, has a pale-ish comb, has a small (about marble size) lump in her neck/throat, is a little lethargic and has a droopy tail. She has her days where she doesn't eat but most days she does. I give cottage cheese & eggs, other stuff she likes to keep her eating. They're on organic layer feed with chicken conditioners added (1 that is extra protein & 1 that is for show birds with vitamins) which seems to help but some days she is just sick. Also, when she leans over goo comes out of her mouth and when she's looking real bad she'll breath weird like her neck is inflating. I have checked for sour crop (it's always empty and flat), she's been wormed, and they get fresh food, produce, & electrolyte water everyday. Run is clean but I do live where there are A LOT of wild birds. My other bird is fine. Vet said they thought Merricks but this has been going on for a while, same symptoms (no change) & other bird is fine. He also thought cancer. Any thoughts guys? Sorry this is so long just trying to be thorough. Thank you

 

Thank you I appreciate that