It's very possible the remaining chin is territorial, I had a pair years ago where the female prevented the male from eating or drinking. I didn't know anything was wrong (water was going down and food was being eaten) until I came home from school to find my male collapsed on the floor of the cage from dehydration. I rushed him to the vet and managed to save him, but I separated them from then on. That is one reason it's a good idea to have as many food bowls and water bottles as you have chins in the cage. The way I have my current cage set up I have a food bowl, water bottle and hay holder on the top and bottom of the cage.
However it's also possible that your female that died had stopped eating on her own, due to some unseen sickness or injury and since you had 2 in a cage you just didn't notice. That does seem to be one drawback of having more then one in a cage, it does make it harder to monitor food and water intake and poo output.