What is the temperature in the tank? What is your tank substrate? Have you noticed a change in your water parameters? What size aquarium are you using? What sort of filter are you using? How long has it been since she ate? The more information you provide, the better equipped we will be to try and discern the problem.
If it's too warm or too cold, axolotls have a tendency to go off of food. If you have a gravel substrate it's possible that she may have swallowed a pebble. That might lead to a throat injury or intestinal blockage. Over-filtration can lead to stress and loss of appetite. As a lake-bottom species, axolotls are not fond of strong currents and such stresses can serve as a gateway to other problems.
Worst case scenario, your axolotl may have a bacterial infection. Bacterial infections can sometimes lead to a decrease in appetite, which is how I lost one of my juveniles. It went off food and had to be forcefed, but it was too weak to fully recover and wasted away.
On a lighter note, my leucistic male stopped eating earthworms some time ago. I purchased some Reptomin floating sticks and tried those, which he readily accepted.
