Thanks for the links, this is quite interesting. My best guess is the kitten just died for some reason, or maybe was indeed sick -it was a couple of months old already, not so little. And she may have gone after the other cat's children out of rivalry, or maybe some smell, or whatever.
On a lighter note, that article reminded me of another couple of female cats who gave birth around the same time and usually mixed up the kittens, they kept stealing them from the other and fetching all of them into their own bed a couple of times a day for weeks!
Since this stuff will probably make the day for cat haters, I'd rather mention that I've also seen cats disprove the idea of them having no loyalty or attachment. Once, when I gave a tomcat a weenie, instead of eating it, it went up two flights of stairs in order to give it to the female who was caring for their babies! The most amazing thing was probably when my old dog who had cataracts and could not see befriended a cat (the son of the ones I just mentioned) who actually led him up and down the stairs! He would go right in front of the dog, climb up or down a step and meow, the dog would advance that step, then the cat repeated the procedure. I remembered that when somebody mentioned that cats could not be trained to lead the blind a few days ago when commenting Streaky's doings.