IT can take a long time for the discharge to stop. We had a cocker spaniel with a very bad case of pyometra and it took her months to stop. They need to be on antibiotics for a time but as far as my experience goes some dogs do have discharge for quite awhile after the surgery but not all do it depends on the case. The cocker we spayed had extreme swelling in her vaginal area and the infection in her uterus had been there a long time before they did anything about it. so in her case the months of issues is just clearing up a super bad infection that was left out of control for to long. When you get her sutures out tomorrow ask your vet. I am not familiar with her case so your vet may recommend another round of antibiotics or something like that.