Anal swelling - warning - photo is g

My 15 yo female chin has had this swelling around her anus for several months now. The vet first thought it might be due to infection, she cultured discharge coming from the vaginal area and treated for bacterial infection. The infection cleared but the swelling didn’t reduce.

Also, my chin is spayed. She had a huge uterine tumor 4 years ago and had a complete hysterectomy. She should not be open (as if she is in heat) and having discharge, but she is. This is a new development as well. The...

Anal swelling - warning - photo is g