[Snowbuckets]

As always I'd strongly suggest vets, they're always going to be far more reliable than people on the internet!

With that said, it could well be a scratch thats healing, maybe get her to check the cage for anything that could have caused it? Sharp objects or general irritation - irritation could be caused by allergies (my ham turned out to be allergic to carefresh and animals, like humans, can develop allergies seemingly out of nowhere!) if this seems to be the case, switch the bedding out to simple toilet roll and go from there, the odour control will be awful but its better than having a sick hammy!

Final thing I can think of personally is mites, in which case vet attention will be needed since I wouldn't recommend giving them mite medication without a professional opinion

But again, I'm just a person who's owned some small furries; the opinion of someone who's trained will always be better!