Illness/Sickness: Depression?

One of my axies seems depressed - it's the only way I can describe it. She sits in a corner all day, won't eat, she's listless and can't be tempted out into the open. The only time she moves is when another axie runs ino her or I move the furniture to clean.
I managed to get her to take a few pellets when I dropped them right in front of her nose, but she actively backs away from worms.
The other 3 are all fine, the water is perfect. None of my axies have ever shown any signs of infection, fungus or parasites. All 4 of my axies are 6-7 inches and they are in a 3ft tank.
Any ideas what could be wrong or what I can do? I'm reluctant to fridge her, but the lack of appetite is worrying me.

Have you ever had squabbles at feeding time? I have to separate my two by drawing one away from the other because they're in 'if it moves - it's food!' mode and often accidentally nip each other while eating. It may be that your baby is nervous of getting near the food in case she gets nipped. She may also be very 'shy' - Toothless was like this when I first got her.

You could use a tank divider at feeding time, that might remedy the situation, or you can put worms in a turkey baster and use it to put the worm near her mouth - I do this for Gally, and it prevents the worm landing on the floor and becoming a potential tug-o'-war or nip match prize. She might also be stressed about something - have you recently added something to the tank? Is one of your filters strong? Stress can cause them not to eat, so it may be this.

The other thing I was thinking was space. There's 4 axxies who need about 1ft of space each, and the space their ornaments take up needs considering too - maybe they need a bit more space? Don't get me wrong, 3ft is big, but I've just seen another member whose male became quite aggressive to one of his females, then the owner got a 4-5ft tank and it stopped! Is it a potential room or hide issue? That might cause her to be a little nervous. Axxies may not be big on territory but they do need space to call their own. Maybe she's too nervous to take space too near to the others.

Oh, ps, what is your substrate?

Thanks Petersgirl.
They are on siliconed down sand, before that they were on large rocks, but I'm still findig little pebbles in poop from when they were at the pet shop.
What I don't understand is that she was fine until a couple of weeks ago. I've never had any 'squabbles' at feeding time (I hand feed them worms) and I separate them when I feed.

Nothing has changed in the tank other than the base. What worries me is that she used to be quite bold and agressive - she was always first in line for food. They have 2 resin tree roots and a slate to hide in/under, and hubby will be making a little drainpipe tunnel for them at the weekend as an extra hide. I agree that thier space is a minimum for 4 of them, and if there are peoblems with agression we will get a 2nd tank.

I'm going to try persuading her into a tub and float it in the tank, and try her with some blodd worms this evening, see if she'll take those.

It is a little odd for her personality to change so suddenly...I mean, don't get me wrong, axxies show us different sides of their personality all the time...but if she was previously dominant and has now turned shy...I don't know what else to suggest. Usually Gally is very rambunctious but he has become a little more wary of Tooth and now waits for his worms rather than rushing up as he's realised Tooth is much bigger (and grumpier!) than he is - we've never had any aggressive nips or wounds though, so I think the fact she's humungous compared to him is acting as a deterrent!

Did the tub method work okay? I was thinking other people might use it if they're having the same issue.