With how you describe it I would do an ET, but sooner rather than later. Save up aggressively and go for it (assuming you have an awesome repo-vet and understand the potential negatives of an ET, etc.). What I’m saying is I wouldn’t wait until she is 15, because you are looking at about 4 years of waiting on that foal (if you start horses in their three year old year). Unless you have other horses to ride while you wait for baby to grow.
Your safest bet, of course, is to look for similar bloodlines and buy something on the ground.
I’m pretty sure my filly’s mom was 13 when she was bred for the first time.
Like someone said, if nothing else, get a reproductive exam done and maybe you will find something that makes all this wondering a non-issue.
