So sorry to hear of your ordeal and trying to get your sweetie some help.
It must be very frustrating.
Has she been checked for gape worms which get in their throats?
Since shes a house goose...do you smoke?
She could be allergic to something in the house.
Also this is a bad time of year for it but she needs sunshine
as much as possible.
If she was mine I would get her on probiotics and Avia Charge 2000
supplement to build her immune system.
This supplement is available via Strombergs.
http://www.strombergschickens.com/
I would also try Vet Rx.
This product has been used for over 100 years. Used in controlling colds, roup, respiratory problems, scaly legs, and eye worm. Many people also use Vet RX to treat their birds before and after taking them to shows. It is safe for all chickens, ducks, turkeys, geese, and game birds. Easy to follow directions. 2 oz bottle.
Some people think its snake oil but for occasional
upper res. I've had with chickens, coupled with Avia Charge 2000
(I highly recommend) it does the job.
If nothing more the Vet Rx might help her breath better.
Also give her as many dark greens as you can afford to buy.
Most of those veggies you are feeding her are high starch and
lacking in nutrients when compared to greens.
Think romaine, mustard grrens, spinach, chard, kale...
not iceberg lettuce.
Dandelion greens are super nutrient dense when available.
I would also feed her raw apples and baked squash or sweet potatoes.
See if you can get her to eat a
little bit of grated raw beets but
don't over do on the raw beets. If she refuses these new food
keep trying.
Have you tried dry oatmeal?
Best wishes.
I hope this helps