I'm actually more worried about the gills. They appear to have gotten stringier; is she going for air at the surface a lot?
I had a golden axolotl that turned significantly paler and lost his gill quality because of an infection inside its gills.
As it's more difficult to breathe, they might become paler, due to less oxygen in their body.
If no one else has any better idea, I'd say your axolotl could do with some salt baths.