Powerful ballad captures Beatrice's heart (6)
I believe the answer is:
strong
'powerful' is the definition.
('strong' is associated in meaning with 'powerful')
'ballad captures beatrice's heart' is the wordplay.
'ballad' becomes 'song' (I've seen this before).
'captures' is an insertion indicator.
'heart' says to take the centre.
The centre of 'beatrice' is 'tr'.
'song' placed around 'tr' is 'STRONG'.
(Other definitions for strong that I've seen before include "curator" , "Forceful" , "firm" , "Great in power" , "Resilient" .)