We are not breeders either. Her heat cycles last a little longer than they should, but not crazy long. I have been told that it really helps to spay. I will do some more research and see what the vet has to say about all the other options, and go from there.
If it is not a really invasive or unsafe surgery, I don't see why it would be such an issue. Horses are gelded all the time. I have no problems with sterilizing mares: If it is safe to do so. Sure cuts the chances of an OOPS baby.

http://standardbredhorses.yuku.com