The sore/wound is back with a vengeance??

https://imgur.com/a/yye0a

That's what little Gouda's butt looks like right now. I just cleaned it and applied neosporin before I took the picture. She gets along fine with the other mice, and doesn't seem to otherwise be showing any signs of distress or illness. Also, none of the other mice have these sorts of wounds.

What is making her do this and what can I do about it? Do I just keep cleaning it and hope it heals? She also doesn't seem to be in a lot of pain from it as she lets me clean it without much fuss and isn't limping or anything. I'm kind of at a loss. She's young and otherwise healthy, just has this thing on her butt!

Update: It almost looks like she was attacked by something, now that I look at the wound closer. The only thing is, there's no animals except for my eight female mice in this house. I am keeping an eye on her and the others because if one of the other girls is so aggressive she is causing these sorts of wounds, she has to be isolated before she ends up killing a roommate. I'm still going to treat Gouda with washing and neosporin twice a day until it heals fully.