Female stars do it, dropping in (3)
I believe the answer is:
she
'female' is the definition.
('she' refers to a woman)
'stars do it dropping in' is the wordplay.
'stars do it' becomes 'shine' (stars shine).
'dropping' indicates named letters should be taken away.
'shine' with 'in' removed is 'SHE'.
(Other definitions for she that I've seen before include "way to refer to mare" , "Female pronoun" , "- - Loves You (Beatles)" , "Female person" , "lady" .)