Hi there and thank you for using Petco Pet Education Center, formerly Petcoach to address your concern. From the photos you provided, this could be a bacterial and / or fungal infection. This area commonly stays moist and can develop a skin infection because of this. I would recommend using Malacetic Conditioning Spray (can be found online) and apply to the area twice daily until resolved. I would also recommend using a steroid spray (Petco has a spray called Well & Good Hydrocortisone spray) and apply twice daily as well to help relieve inflammation. If this does not resolve or it worsens, I would recommend having a veterinarian examine her so that the most appropriate diagnostic and treatment recommendations can be made. I hope this helps! Please let me know if you have any other questions or concerns and I would be more than happy to help you further.