Hello Jackie,
This is Dr.Christian. There is no harm in having her spayed before her first heat and in fact that could be significant harm in letting her have the first heat. Studies have definitively shown that a dog spayed before her first has almost no chance of malignant breast cancer later in life. Even one heat cycle increased the chance of breast cancer significantly. Studies have also shown that spaying before the first does not cause any problems. If you have more questions please let me know.
Veterinarian
12 years of veterinary experience in medicine, surgery and behavior with exotics,canines and felines