Hello matthewC,
I can't see your axxie's tail very clearly, but I can see pinkish bits there. This looks like either a bite or a tank injury - is she (I'll assume a 'she' until I can see a tail bump) in with other axolotls? Could she have caught it on an ornament or in a filter?
Either way, it doesn't look serious. If you begin to see fluffy, cottony bits that don't brush off when you touch them, then you might have fungus on your hands. If it's just skin that looks a little red or dead skin, then you have the choice of either leaving her in her current tank, feeding her regularly and keeping an eye on her temperature, or tea bathing her.
Tea baths tighten the axolotl's pores, preventing further infection. They also kill bacteria, clean wounds, soothe the slime coat and promote calm for most axxies. I had a male with a severe head wound and it fixed him up in two days!
If she is on her own you can add tea to her tank with no worries. Sometimes people remove them from the tank if they are with others to prevent the spread of infection or to ensure none of the others have a reaction (which is extremely rare in any case; I've only ever seen it once and I am dubious about that one case). All you do is take a regular (not herbal or fruit) tea bag and add hot water in a dark mug (I say a dark mug because the tannin will stain any lighter mugs). Allow it to go cold and voila! Add the tea to your tub or tank for a tea bath. You can top it up as you do water changes if you like. It's just an added extra if you are worried or if you think she's just not healing as quickly as you'd expect.
