I don't recommend any medication because the mouse will groom herself and end up ingesting the med. Use a small swab and clean the wound (no peroxide please, it's very irritating to the tissue). Separate her from the other mouse/mice until she heals up. Keep an eye on the wound for any signs of swelling or oozing. Most mice heal up pretty well from bites like this. If you want to reintroduce her to the colony, try mixing some of her bedding with the other mouse/mice bedding so they can get used to her smell. It takes a bit of time but it often works.
If a cage is overcrowded, they will attack any newcomers. I don't know what your set up is like. In a 10 gallon fish tank I only keep 1 male and 2 females at a time.
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