What feed was she on?
There are a lot of things that could cause this, the amoxicillin may help but it’s critical that she eats.
If you have any banana take a 1 inch sized piece, moisten it, apply pressure to the corners of her mouth until she opens it, then shove the banana down her throat as far as you can get it, then gently massage her throat. Banana is fattening and will strengthen her heart and it slides down the throat easy when it’s wet.
If you don’t have the supplies to tube feed her you should get them asap, if a feed store doesn’t have them a vet will,
Amazon usually also has them.
You’ll need something like these
https://www.amazon.com/Pieces-Rubbe...-3-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&psc=1
https://www.amazon.com/Pack-Syringe...8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1
I’m not sure where you are but if you can get a high protein start feed that would be best, something like purina 30% game bird start. That usually isn’t great for geese but it’s perfect as a recovery formula.
Instructions on how to make syringe formula.
Take a little of the start feed and mix it with boiling water in a cup, it expands as it soaks so you may need to keep adding water or it will get too gummy, it needs to stay soupy. When it’s cool enough to stick your finger in it without burning but still warm add some vitamins to it, you can also add probiotics. While it’s still warm suck it up into the syringe or pour it in, try to keep as few air bubbles as you can out, this can be a bit of a hassle, fill all 60 ml.
Then apply the tube, dampen the tube with a little water, squat over her back but don’t sit on her, you just want to use your body to restrain her. With one hand apply pressure to the corners of her mouth until it opens, open her mouth and insert the tube down the RIGHT side of HER throat and slide it down, you’ll see a little bulge on the right side of her throat and if you can’t see it you should feel it slide down.
When the end is near the base of her neck hit the plunger until it’s empty.
The faster you feed her the less stressful it is for her and she’ll struggle less.
Two feedings a day will keep her alive, three to 4 will start to put weight back on her. You want to wait at least an hour and A half between feedings.