Girl, not quite eight, reportedly in charge (7)
I believe the answer is:
mandate
'charge' is the definition.
(I've seen this before)
'girl not quite eight reportedly' is the wordplay.
'girl' becomes 'manda' (**).
'not quite' means to remove the first letter.
'reportedly' shows a homophone (sound like).
'eight' sounds like 'ate'.
'ate' with its first letter taken off is 'te'.
'manda'+'te'='MANDATE'
'in' is the link.
(Other definitions for mandate that I've seen before include "Authority conferred on a tandem" , "Authority to act" , "Official order or commission to do something" , "Authorization, official instruction" , "Order - charge" .)