Alot of bigger ranches prefer to ride and work geldings, because they don't have to deal with heat cycles or other 'hormonal' issues. If you're doing long days of work, I could understand why you wouldn't want to deal with those!
I probably wouldn't suspect anything, really, of a broodmare who's never been broken in\trained, as I would get a vet check anyway. You can ask about her offspring, as that in itself will give you an idea of how she may be as far as trainability, as the baby is half her!
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."