The primary rule-out for Dolly is a pyometra, a common problem in middle-aged to older unsprayed female dogs.  The hormonal influence during estrus causes engorgement of the lining of the uterus.  At times, it fails to fully regress.  The uterus is usually a sterile environment, but bacteria can move up from the vagina into the uterus and the situation is perfect for an infection to develop.  Typically, the cervix closes after estrus and the infection "brews" in a closed "container", known as a closed pyometra.  Occasionally, the cervix stays open a small amount and there will be a vaginal discharge.  This is known as an open pyo.