Off her food and floating

Heya,
I was recently given an axolotl by a university technician when they found they didn't need them any more. She's about 5 years old.
I got her on the Wednesday morning and fed her in the afternoon. She took a couple of slices of squid quite happily with no regurgitation. However since then i haven't been able to convince her to eat. I've tried both the squid and the pellets they were fed at the university, as well as a second brand of pellets and live worms. She'll look at the food sometimes open her mouth a little, but then she'll make up her mind and just back away and find a place to hide away.
It's now been a week and a half since she's eaten and i've noticed she's taken to floating at the surface. She can get back down again, but it's really starting to worry me.

The water has been kept around 18'c although it's fallen to about 16'c over the last few days.

Any advice would be appreciated

Has she ever been kept on gravel? What are your ammonia, nitrite and nitrate readings?
Temp is fine
Mel

I just tested the water and it's come back
with 10 for NO3 and 1 for NO2, GH reads 8'd, KH reads 6'd, pH is 6.8, and 0 for chlorine.
I've also been replacing a 10th of the water every day to keep it clean.

There's no gravel in the tank, only large rocks, all much to big to swallow. I just don't get why she'd behave like this

It's now been two weeks since she's eaten >.<
I think her gill is looking a little less feathery than before but it's hard to be sure. There also seems to be some minor peeling or maybe just lose skin or something around her lips.
Any suggestions are welcome :/

You've tried live worms? That should be the primary diet...and has she been producing any waste?