as i gather it there are two ways:

one is to just keep trying and trying until she really is developing eggs.

the other, used by some advanced breeders, is to use ultrasound machines to regularly measure the follicle size. then you only pair when the follicle size is just right. its really advanced, because the machine is expensive and using it to get correct measurements of follicle size takes skill and experience.

both strategies seem valid, because some of the really big and professional breeders use one way and others use the other way.