Unless she's truly stellar, it might be more trouble and risk than it's worth. You can buy a weanling for a lot less risk and cost than getting this mare in foal.
Now, if she is truly an outstanding individual in temperament, breeding, and conformation, the easiest way to get an older mare in-foal is live cover. It comes with its own set of risks, but the success rate tends to be higher. Many breeders will do a breeding soundness exam, and if all is well, simply turn mares like this out in a broodmare band with a stallion to pasture breed, and if she settles, great. If she doesn't, her likelihood of settling with AI is near zero.
Now, if she is truly an outstanding individual in temperament, breeding, and conformation, the easiest way to get an older mare in-foal is live cover. It comes with its own set of risks, but the success rate tends to be higher. Many breeders will do a breeding soundness exam, and if all is well, simply turn mares like this out in a broodmare band with a stallion to pasture breed, and if she settles, great. If she doesn't, her likelihood of settling with AI is near zero.