The girl's got a fifty in history (6)
I believe the answer is:
annals
'history' is the definition.
(annals is a kind of history)
'the girl's got a fifty' is the wordplay.
'the girl's' becomes 'anns' (woman's name).
'got' indicates putting letters inside.
'fifty' becomes 'L' (Roman numeral).
'a'+'l'='al'
'anns' enclosing 'al' is 'ANNALS'.
'in' is the link.
(Other definitions for annals that I've seen before include "The Four Masters wrote them in 17th century" , "Registers" , "Chronicles" , "History of events year by year" , "Tomorrow (Spanish)" .)