Sorry for the confusion. Spayed dogs cannot get pyometra (which literally means pus in the uterus). Unless the spay was done incorrectly and some of the uterus left in the animal. This is rare and I wouldn't worry about it.

In short, dogs are reproductive machines. If in the wild, they cycle and breed etc. This constant estrus cycle promotes what's called cystic endometrial hyperplasia or basically a thickening of the lining of the uterus. This condition (which shows no signs and is by itself not a disease process) is promoted by the estrus hormone progesterone. It basically sets up the scenario for a uterine infection. Since the cervix is normally closed (or sealed) until partuition the infection essentially progresses in the uterus making the dog sick. There are cases (less common) called an open pyometritis in which the pus actually leaks from the vulva and stinks.

Pregnancy reduces progesterone exposure thus dogs that breed regularly are "protected" from pyometra. This does not mean that a retired breeder cannot develop the condition. Surgical correction for pyometra is to spay the dog, however, this is never routine. The uterus is filled with pus and bacteria and often fragile and at risk for rupturing in the abdomen (before and during the surgical procedure). Clinical signs of pyometra include acute inappetance, lethargy, enlarged abdomen (not always) and increased thirst and urination.

You spayed her at 9 months and I think that was great. Her risks for mammary cancer are slim to none and you don't have to worry about her estrus cycle interfering with the hunt or emergency surgery down the road.

Regards,