Females don't typically reach reproducing size until 17". Occasionally it can happen when they are smaller, but I wouldn't allow this. I generally prefer them to be at least 18", if not 20", before I will let a male have access to them. Egg production takes a lot out of them and it is harder on a smaller female.
I suggest keeping them separate and feeding up your female for another year or two to put some size on her before allowing contact with a mature male.
Why breed them anyway? Just saying they're a dime a dozen . Rescues are full of them . I would hold off let the demand pickup . But Thats just me . If you want to get into breeding tortoises breed one that is being collected wildly to help stop the importation of said species. No offence to you guys who are breeding sulcatas .