UPDATE on Fiona/sick chicken.
So we kept Fiona in and gave probiotics, electrolytes and antibiotics for a few days. She seemed to remain about the same and maybe got a little better. She did start loosing ALOT of feathers so I thought maybe it was just a hard molt. Her crop felt ok and nearly empty in the mornings so no apparent crop issues. Went ahead and put her back out with the other chickens but she's continued to lose weight, sometimes weak, and then about a week ago her crop did not seem to be emptying as usual anymore. Brought her back in and spent the week massaging her crop, trying to empty it a couple times (no success) and doing the usual things for it (grit, water, massaging). Did not feed her over the weekend and it has gone down significantly but remains full and hard. Took her back to a (new) vet and she is now scheduled for her crop to be surgically cleared this Wednesday. However, the vet mentioned mareks and feels maybe the crop is just a side effect of something else (maybe mareks maybe not). But wouldn't she be dead already with mareks? She's been like this for over a month. She was rechecked for parasites (none) and this time got blood work (results pending). Also was given de-wormer to give in case.
Not sure I have any questions other than maybe how quickly mareks kills. Just an update and quite frustrated without knowing what's going on. This vet was much better and just grateful I have one to take her to but regardless both said it's just too hard to know what's wrong. Feel like I just need a good, experienced farmer instead of these vets. This will be the first crop surgery this vet will do so fingers crossed for this! She is going to research and call fellow vets to make sure she will do it right.