Just looks like a small wound. She might have caught herself on the wood when being chased by a male. It should heal up in a few days. Monitor and post another picture if it gets worse.
You can reduce the chance of infection by doing a big water change, gravel cleaning the substrate, and cleaning the filter (if the filter hasn't been done in the last 2 weeks).
You can reduce the chance of infection by doing a big water change, gravel cleaning the substrate, and cleaning the filter (if the filter hasn't been done in the last 2 weeks).