I know the thought of surgery is scary, but just remember that by spaying your female dog early, you can all but eliminate the chance of her getting mammary cancer later on.
In those females spayed prior to their first heat cycle, breast cancer is very, very rare. The risk of malignant mammary tumors in dogs spayed prior to their first heat is 0.05%. It is 8% for dog spayed after one heat, and 26% in dogs spayed after their second heat. http://www.peteducation.com/article....&articleid=460
So please, for the sake of their health, spay early!