Margaery is older than Tommen, presumably old enough to rule in his stead if he's still not considered quite old enough. There's no reason for a Regent anymore with Margaery in the picture, anyway.

There is obviously need for a Hand, but it doesn't seem like a female Hand is the done thing in Patriarcheros.

Cersei is chairing the Small Council by sheer force of will at this point - I think Tommen and the (remaining) members of the SC just haven't found the balls to tell her to clear out. Tommen could have her on the road to Casterly Rock at a moment's notice if he was gutsy enough to tell her.

>until the king comes of age, thats what that status is about,
>marriage is irrelevant on that front but that might be how
>they have it set up on the show
>
>