To sterilize or not?

As an animal rescue person, I am always in favor of early spay/neuter of all pets. But, I can see your dilemma. The number one reason to spay your dog is the health benefit of reduced incidence of mammary tumors which is the number one malignant cancer in female dogs. Studies have shown, that as long as a dog is spayed by age 2, you can greatly reduce the risk of these tumors forming. Of course, the other obvious risk is also when she is in heat, she escapes and mates with another dog and you end up bringing 6 more mutts into the world. If your dog is not the perfect size for her breed, then breeding her is probably not a good idea anyway for the future of the breed.

Its your choice. I applaud you for doing the research and asking questions about it. An informed decision is always the best.