Your axolotl isn't looking great, but axolotls are tough, fortunately. Sometimes axolotls won't eat for a few days, especially after a change - they can go for quite a while without eating.
First, the best place to post this is in the sick axolotl forum, since you will get a lot more knowledgeable people looking there. That forum is
Axolotls (<i>Ambystoma mexicanum</i>) - Sick Axolotl? at Caudata.org Newt and Salamander Portal
Next, you did the right thing by getting her into a new container and changing the water. But I am wondering if your water was really the cause of the gill problems. So, question time:
1. Did you buy her at a local store or was she shipped to you? If she was shipped, do you know he long she was in transit? (I am wondering if ammonia build-up in the bag or lack of oxygen is the true cause of if the filament loss.)
2. Did you dechlorinate the original water in the 10 gal tank? If so, with what product?
3. What temperature is your tank at?
4. What chemicals did you suspect were the problem in your tank?
Next, how experienced are you regarding aquatics in general:
4. Are you familiar with "cycling" a tank? (Monitoring growth of good bacteria to convert ammonia and nitrite to nitrate, etc..)
It is good that you have test strips, but a liquid test kit would be better. Also, you need a test for ammonia. It is hard to figure out the readings from the pictures - it looks like your nitrite is not zero? That isn't expected in a brand-new tank set-up.
5. Is this a new tank or a tank that is already cycled?
Regarding her not-eating:
6. What are you trying to feed her and how?
It looks like her arm has been injured. Fortunately, axies heal well.
7. Was her arm moving properly when you got her?
Frankly, I think your axolotl wasn't in the best of shape when you got her. The best thing now is to try to keep the water conditions perfect and allow her time to heal. If your tank isn't cycled, that means daily large water changes, or keeping her in a smaller container with 100% daily water changes, using an appropriate dechlorinator. Keep the water cool - a fan blowing across the top will drop the temperature a few degrees below room temp, usually. Remove uneaten food so it doesn't foul the water.
We'll help you out however we can. :happy: