Rowling initially overwhelmed by Potter: she writes adult novels (7)
I believe the answer is:
drabble
'she writes adult novels' is the definition.
(Margaret Drabble the English novelist)
'rowling initially overwhelmed by potter' is the wordplay.
'initially' indicates taking the first letters.
'overwhelmed by' indicates putting letters inside (inserted letters get absorbed or overwhelmed).
'potter' becomes 'dabble' (both can mean participate in superficial way).
The initial letter of 'rowling' is 'r'.
'r' going into 'dabble' is 'DRABBLE'.
(Other definitions for drabble that I've seen before include "Make dirty; Margaret --, author" , "Margaret -, English novelist" .)