Am a little concerned by your comment "you think it would do her good' to have a foal?
It's not necessary for any reason for a horse to HAVE a foal. There are so many unwanted horses out there, I believe you have to be very cautious about breeding at all. I would only breed if I was to keep the foal myself (which I am) or had someone I trusted who desperately wanted a foal from a particular mare.
Please don't breed just because you think it would do her good