Hi,, I bought a moggie very cheaply from a pet shop. I was told she was cheap because she was a little older than the normal kitten that they sold. I was told she was 10 to 12 weeks old.
I waited a couple of weeks to take her to the vet for check, microchip, vaccination and desexing. When I did take her there, I was told she was about 18 weeks old and that the fat little ball of fluff was actually heavily pregnant and due any day to have the kittens. The vet suggested desexing while she was pregnant because the world already has enough cats. Despite feeling terrible about ending the lives of the unborn kittens, I agreed to the desexing. That was 4 years ago, and I still have guilty feelings about ending the lives of those little kittens.
What I'm getting at is, .......maybe she's pregnant.
Good luck
There is nothing normal about enlarged mammary glands in a
kitten that has not had a heat cycle.
If she is truly 4 months old you need a second opinion.