Sorry girls, you've been mis-informed. There is no difference in the risk of uterine cancer between breeding and non breeding does.
Our vet spays hundreds of rabbits for us each year. Almost every one over the age of 4 has the start of uterine cancer! It does not matter if they have never had kits or have come from a breeder. They ALL have it.
She has even seen the start of it in 2 year olds.
Most vets (ours included before she started spaying so many for us) have no idea of the scale of the problem. Very often the rabbits die without showing any symptons so it goes undetected.