The one that died would have been a runt, not a peanut. Runts are normal, but undersized. Peanuts occur in the dwarf breeds and have a genetic flaw that usually results in death within days. An important distinction.
Does do vary in the number they can effectively feed, but it is not totally dependent on the number of nipples. Kits move around during feeding so usually any kits that are strong enough still get some milk. The problem is that one that gets shorted can get too weak to compete in a large litter and falls further behind. Sounds to me like this may be the situation here.
Some people cull, some people let nature take its course, and some people give the kit a supplementary feeding or two by flipping the doe over and letting the kit nurse.
Actually, I much prefer a doe that produces a consistent 6-9 kits per litter. They grow better and there are fewer losses and no need to intervene.