I am sorry, really not trying to step on toes here. I probably have more experiences in births and birthing problems than most if not all on this thread. Here's the first couple of things that come to mind. The cat could've gone into labor and since the kitten was so big, gotten stuck haulting the labor, pinching the cord or already seperated afterbirth, killing the kitten and the labor never progressed. In this instance, the kitten could've also slipped back further into the uterus as well so even checking the birth canal or how seperate the hips have been wouldn't help pinpoint that. Another scenario, the kitten could've died in utero, then the infection started because of the dead kitten. She could've been slightly dialated and an infection could've "snuck" in that way, where as the kitten could still be alive if the infection hasn't killed it yet. The cat could've never gone into labor in the first place because there was only one kitten, sometimes that happens with an animal that usually produces more than one fetus, and then the kitten died and the infection started. There are so many possabilities to the start of the infection. A vet really needs to take a look, check the kitten for viability, and give the owner her options. We have NEVER had to spay an animal because of infection. We did have to spay a dog because of a phantom pregnancy where she ended up with mastitis that would'nt go away, put a goat down because of a torn uterus, we had a misscarriage on Christmas morning that was not so fun, of almost full term quads mind you, but never an infection so horendous the animal had to spayed. I have learned that almost every species' birth is just like another. However there are species that do fine birthing back feet first and some don't and a few other differences, minor differences. And don't get me wrong, we've had about 15 cats give birth on the farm and in the house, I'm just trying to say that I am not a novice either, I have so many birth experiences, but cats are way down there on the totum pole of my birthing experiences. I've always wanted to be a vet and have read and studied many books along with all my experiences and still have neighbors and old friends even from high school call me long distance to ask animal questions. However noone can know exactly for sure what is happening with this cat, therefor, all we can do is give our own personal experiences in relation to hers and hope for the best. We cannot diagnose anything on the internet, she just needs to find another vet. I'm really not trying to sound snobby, just wanted to reinforce my credibility. What I can do, if she hasn't done anything about the cat yet, though hopefully she has or the outcome looks pretty bad, is contact the vet I chat with via e-mail or home number and give her the info, but like I said, the cat needs tests and still, though she is a vet, the vet would be speculating on possibilities.