Eleven is a large litter but she will likely handle it. I'd give her some kitchen oatmeal as a supplement to help her with milk production and give her all of her regular feed that she wants. The kits move around and switch teats as they feed, so usually they all get fed. If there are one or two that are weaker and cannot compete you may lose them, but generally speaking the doe's milk capacity adjusts to meet the demand.
I've never taken extraordinary measures to help the weak ones survive. Once or twice I've seen kits so tiny compared to their siblings that I did not see how they could compete. But they did.