it's being mishandled by the writers

but the reason she was ruling while incest-Joff was shooting broads with crossbows is bc he was too young to rule/marry

old enough to marry = old enough to rule

the problem is he's not ruling...he's giving zero orders nor delegating so the "Queen Mother" is out doing whatever she wants while claiming to speak for him...

so she has the same role but no longer the same title...she's behaving more as a hand at this point