[cypher]

It does look a bit red, hard to tell from a photo though.
Is she living alone or with another of your hams? I think from your previous posts she's alone but if not then fights are always a possibility.
She might have caught it on something if she's been digging around in the cage, does her cage have bars? If it does then pushing it through the bars or bar chewing could cause a problem like that.
I would check her cage over for anything sharp or rough & keep an eye on it, if it doesn't improve then get your vet to have a look.