There are no drugs that will produce a breedable follicle. With your mare's age, there are two major concerns: first, her having a normal estrous cycle and producing a fertile follicle. With this mare, it is important that she is in good health and weight, as this will give you the best chance of her having viable follicles.
The next concern is the health of her uterus and cervix. By this age, the uterus may have undergone changes that can be age-related and potentially health-related (if she ever had any uterine infections related to previous foalings or poor conformation). The integrity of the cervix may also have been compromised from previous pregnancies. To determine your mare's potential to ovulate a viable egg and produce an embryo that can be maintained to term, a breeding soundness examination by a veterinarian who specializes in reproduction would be advisable. If it is determined that your mare is producing viable follicles, but her uterus is not likely capable of carrying a pregnancy, embryo transfer can be a consideration if your breed association allows.
