[Tink]

How sad!
Luckily, I have had no experience with this. I've heard of it... just barely as one of the reasons that they've changed the recommendation of breeding on every heat for a shorter time and then spaying a female rather than the skipping of every other heat. It seems that a heat not followed by pregnancy is the opportunity for this to develop.

There is an alternative treatment of antibiotics and medication to make the female expel the pus like she would pups... but it involves a lengthy hospitalization and is less sure than the surgery. It is usually reserved only for show dogs that are worth MEGA bucks and have little value if spayed.

I hope all goes well!