I would go get a breeding check done by your vet and see if her vulva can handle a foal. If she hasn't been bred in a while, she might be hard to settle, so start around Feb. To breed, that way if she settles you will have a Jan foal, if she doesn't you can keep trying until May/June. I'd say if the vet says she's OK, go for it!! But remember that even really well bred horses are selling dirt cheap right now(if they sell at all), so reconsider breeding if you plan to sell. If you're going to keep the foal whether its a filly/colt, then go for it!