Illness/Sickness: Female Axolotl losing gills

Hi, I am really stumped and hoping someone can help.

My adult female has lost the majority of gill feathers on the middle 'stem'. She is eating well (earth worms and blood worms for occasional treats) swimming around and generally looks fine.

The water parameters are good:

Ammonia 0
Nitrate 20
Nitrite 0
pH 7.2

Temperature 19 c

There have been no changes made in the tank and my other two adult males are fine and no signs of losing gills. I have had all three for about a year after adopting them from a friend.

I have read previous threads about this on here but haven't been able to find an answer.

Does anyone have any idea what could be causing this, should I be worried and what is the best course of action?

I have attached a photo of Bette to see the loss.

Any assistance would be greatly appreciated.

I had that same experienced with one of my albino breeder male ( even worse than yours cause there were no gills whatsoever) with no everdence of bad water or anything toxic and all 0 with 7ph So my last conclusion was that there must have been some kind of un seen fungus spores , so I tired tea bath , nothing happen, I tried regular salt bath , nothing happen . Then I tried a drop of melafix right on his gill, suddenly I begin to see one little single gill fan out a little but it was so small like a thin 1 millimeter round pink dot of gill. So if melafix can relax one gill out , meaning there's hope yet. The next day I put him in another tub with aquarium salt and let him sit it in all day in cold room ( not fridge) then I starting to see change his gills and starting to show some gill buds growing like cherry blossom. So I put him back in the tank and added aquarium salt in to tank every day with melafix. He started to look better after a few day, the week after I've got some more Indian almond leaf extract and added more beneficial bacteria . He is back!! His gills now still short but looks very healthy. I wish I did took a before and after shots . So try melafix to see if your axie gills would responding to it first. If we're right about this then just do what I did.

Thanks for the advice.

I'll give Melafix a go and see if that helps.