An bhfuil bean ghrinn ann?
Like the priesthood clowning is traditionally an all-male preserve - I think that's where the resemblance ends ... Anyway, I suppose you are right. In this era of comhionannas (equality) I don't see why we shouldn't have mná grinn - it's just that I have always found clowns sinister and completely unfunny and personally I would rather have nothing to do with them, male or female. But if people insist in immersing themselves in the dark and scary world of clowndom, for a woman it would be:
An bhean ghrinn, the female clown.
Don bhean ghrinn, for the female clown.
Scéalta na mná grinn, the stories of the female clown.
Na mná grinn, the female clowns.
Na mban grinn, of the female clowns.