Playing Lydia, Glenda is a star (7,4)
I believe the answer is:
leading lady
'is a star' is the definition.
(I've seen this before)
'playing lydia glenda' is the wordplay.
'playing' indicates an anagram.
'lydia'+'glenda'='lydiaglenda'
'lydiaglenda' is an anagram of 'LEADING LADY'.
(Other definitions for leading lady that I've seen before include "Heroine - gaily landed (anag)" , "a star" , "Female playing main part in play" , "Film" , "Female top of the bill" .)