You seem a little confused about your cat's anatomy. It is very much like a human's anatomy.
The ovaries are where the egg comes from, it is then fertilised and the kitten develops in the uterus.
If you are unsure of pregnancy see the vet, also if only 1 nipple enlarged I would certainly take her to vet as it could be much more sinister than pregnancy.
Hope she is fine and well.
She needs to see a vet. This could be an infection or even a tumour or just something to do with her pregnancy (if she is pregnant) Please get her to a vet asap, she needs a proper examination.