My guess, since the fluff didn't respond to anti-fungal treatment, is that it's bacterial. Even if the fungal treatment was harming the axolotl, you should have seen it have some effect on the fluff if it was actually a fungal growth.
Did the plants with the snails also have fish in the tank with them, at the store they came from?
When the other axolotl died, did you do anything to clean/disinfect the tank? The plants could have introduced the disease into the tank- it's always a good idea to quarantine new plants just like you would quarantine new animals. Plus then you can pick off the snails you see before they get loose in your main tank and take over
The fungus in the mouth looks to me like a classic case of columnaris infection. Columnaris is a bacteria that likes cold, uncirculating water. It's nasty, spreads quickly and is hard to get rid of. In fish it usually takes hold around the mouth and gills, like on your axie, but some people have also had it on their axies around wounds on the tail or legs. The fact that it's not responding to salt baths or fungal treatments, AND is continuing to spread in cold water makes me think columnaris could be a possibility. It isn't spreading like wildfire though, from what I can see in the pictures, so it could still be something else. If you do a search on this site for "columnaris" you'll find a number of other threads where people have had similar troubles. I'd go down to your store and find some medication SPECIFICALLY made for columnaris and give that a try. I'd also get her into her tank again, somewhere where there's some circulation (take the carbon out of the filter!) The 14 degrees you said her tank was at is a nice temperature for them to live in normally, so should be ok for the bacterial treatment. Putting axies in the fridge salt baths fixes almost all of their problems most times, but the salt and fridge aren't helping here- it's still spreading.
Skin shedding could be a normal response to something like poor water quality. Because toxins like ammonia and nitrite in the water burn their skin, it's normal for some skin to become damaged if they're kept in poor quality water for too long. When those bits of skin die they'll flake off, just like your skin does when you have a blister that heals- the new healthy skin is underneath. Quite often the stores that sell them don't keep their axolotls in optimum conditions, so this could be causing her flaky skin... how long have you had her? It could also be that you're seeing an excess production of mucous. The fungal treatment you used and the salt baths can both irritate their delicate skin, which isn't always bad. Since the mucous coating is a natural protective layer, an irritation that causes a little more mucous to be produced isn't always bad. Sometimes it can help the skin heal. Hard to say what it is without really seeing it first hand!
Frenesi looks pretty sickly though, so the flaky skin could be just another sign of her ill health, it's hard to say. She's really very skinny, and with the fungus in her mouth I doubt she's been feeding much... does she still eat, when not in the fridge? Generally veins showing and redness is a sign of stress, and she's definitely stressed!
I really hope this little girl will get better for you! They're such wonderful animals. Good luck to both of you, I'll keep my fingers crossed!
