A stray cat has given birth to six kittens under my porch. It's an unsavory place for unprotected kittens. So we brought the mom and her babies into our home. For the first day and a half, all was well. Then one of the calico kittens seemed to lose energy and stopped nursing. The other kittens are fine. But the little calico would fight for her place and then not nurse. We have tried a medicine dropped and the hertz nursing bottle. We have gotten replacement formula into her, but she isn't nursing or swollowing on her own, or moving. She lays flat on her side. Under her neck it is slightly swollen and dark. I don't have the money for a vet and I don't want to just give up.

It doesn't sound good for this kitten. If you can't get her to a vet or take her to a shelter so they can take her to a vet, she will die very soon.

By the swelling and possible bruising it sounds as if she may have been injured somehow.
Perhaps by mother moving her, in any event not drinking may be her end if she doesn't get some medical help soon. Tiny creatures have little to no reserve and can go downhill very fast.
I agree that if you cannot afford a vet then her best option is to be turned over to a rescue/humane society.

It hurts to say, the calico passed away right after I posted this. It seemed to have had a seizure and then nothing. My kids and I are sad, but still happy because the other five kittens are thriving. Thank you for your advice.

Sorry to hear this, wishing the other five well.