Going for air all the time, not eating, white stuff coming from the butt

Hello!

I have 340L tank with 4 big axolotls in the age of 8-9 years.
The grey one(female) has always been the most active, eating the most ect,
And now for a couple of weeks she is not eating, maybe she eats some of the pebbles but I have not seen it. Also I have not waited for an hour to see if she does, just don't have the time, I hope she eats some of them. But she is not taking any crickets from me which they usually all love.
Lately I noticed that she had some weird white stuff coming out from her butt.
Also she is all the time going up for some air, which the others are not doing and which she did not do so much before either.
I do not know what to do with her.
I have never but anyone in the fridge and I don't know if my fridge would even be okei for it because the back of the fridge freezes quite often and I can not change any temperature on it myselg and I am affraid to do put her there.
It is also not so easy to get distilled water here which I read is required.

Hello!

If you want to know if your fridge is suitable, it's very easy to test, right? Just put a tank or tub of water in there (as far away from the back as possible), keep it there for a day or so and then check the temperature.
You don't need distilled water for the fridge. It's advisable to use clean water, but tank water will suffice.

Fridging can be useful, but it's not the end-all solution. Maybe it would be better to keep the axolotl apart for a few days first, just in her own tub so that you can keep close tabs on her. That way it's easier to see if she still eats pellets, if she poops, if she looks stressed, etc.

The other three axolotls are fine?
Just to be sure, can you tell us your water parameters (temperature, pH, ammonia, nitrites, nitrates)?

Unfortunately my friend died this night. I put her in the fridge as a last resolution but it did not help. This morning she was gone and I have already buried her.
I feel very sad and hope that whatever she had, my other 3 ones don't.
I can only think that she had a good life in a big tank with her friends, as she lived up to almost 9 years.
She was my favourite and I feel very sad..

I’m so sorry for your loss