How do you tell grandparents when your son or daughter comes out?

My oldest child told me that she is a . I have no problem with it, and no problems with her going to dances or parties with her girlfriend, but my question is, when Grandma sees the pictures of the dance and wants to know why she never sees her granddaughter with a dashing young man... what do or how should I tell her. Should I have my daughter tell her, or just smile and say " I dunno"?