Illness/Sickness: Urgent please help - swollen sick axie

Please we Need urgent help with our sick axie "Sierra". About a week ago our albino axie started to vomit/gag. Originally we thought she swallowed a rock so we took her to the vet for an xray. They found no foreign bodies and sent her home. The vet sent us home with instructions to buy real plants for the tank rather than our plastic ones and feed her a more varied diet other than her usual bloodworms so we went out and brought 2 new plants and crickets. These have been the only changes made, and she did seem to rather enjoy the crickets.
Since we brought her home she has continued to gag. Yesterday we discovered what appears to be fluid buildup/ swelling in her back legs, back of her shoulders, under her mouth and under her belly between her front legs. The lump under her throat is hard and she appears to be unable to open her mouth fully. We have had her in the fridge overnight and have given her salt baths because she has white cottony like threads comming off her gills.
We have had her about 3 months and she is about 12cm long, we have no idea how old she is. Her tank mate "Flaco" is doing well, no gagging and is as frisky and hungry as ever. We test the water regularly and do a 20% water change every week, we feed them in a seperate feeding container so their living tank is not contaminated by left over food. The water PH is constant at 7.2, Nitrates and Nitrites are nil, Amonia is about 0.25ppm.
We will attach some photos of the swollen areas. We just hope its not mouth rot, or worse still heart or kidney failure.
Please help us, we dont know how much pain she is in or what is wrong, we want to help and do not want her to suffer.

I would get her back to the vet asap. Since its not a stone(hopefully you have removed all of those from her tank just in case), you need to find the reason she is not eating and now is bloating, as they likely are related. Some get parasites, some get absesses, etc. which can all cause her not to be able to swallow. Did the vet take a look in her mouth? There are also many posts on here about bloat, and hopefully if you can address the underlying issue causing her to not be able eat, the bloating will reduce as well..

She looks on the thin side, but that may be due to the swelling in her neck combined with not eating for a week. Bloodworms are actually a pretty good staple food for young ones, but earthworms are even better once she's on the mend. Crickets are an OK treat. Did the vet seem axolotl knowledgable? When you head to the vet again, I'd print off that axolotl.org health page which lists axolotl safe and toxic medications and also discusses antibiotics and how to give them. Take that with you just to ensure the vet doesn't prescribe something harmful.