Thanks for using Petco Pet Education Center, formerly Petcoach! This is likely a perianal or anal sac abscess or even a mass. How this is treated, will depend on what it actually is. However, it usually does not represent an emergency. If it is an abscess, drainage and flushing of it as well as antibiotics may be indicated. I recommend that you have her evaluated by a veterinarian when possible if not open today for further assessment and treatment. They would be able to check for these possibilities and treat accordingly. Good luck and have a great day!