Girl playing Hamlet (6)
I believe the answer is:
thelma
'girl' is the definition.
'playing hamlet' is the wordplay.
'playing' indicates an anagram.
'hamlet' is an anagram of 'THELMA'.
(Other definitions for thelma that I've seen before include "Foreign policy of force" , "-- and Louise, 1991 film" , "Woman" , "Charge with gas" , "Louise's friend" .)