If vet stuff is free, I would either short cycle her or in 3 weeks start teasing. When she STARTS to show signs of heat, get her in for a folical check. Checking her folicals daily while continuing to tease is the best way to get a head start shipping semen. You dont want to wait and discover shes at another 50 something.....IMHO. What a mare ALWAYS does is to be inconsistant. That you can count on.
Nice stallion BTW. You should post a picture of your mare. I want to visualize the cross !