Energy encapsulated by lovely flower girl, perhaps? (5)
I believe the answer is:
niece
'flower girl perhaps?' is the definition.
(I've seen this in another clue)
'energy encapsulated by lovely' is the wordplay.
'energy' becomes 'e' (physics symbol as in E=mc2).
'encapsulated by' is an insertion indicator (I've seen this in other clues).
'lovely' becomes 'nice' (both can mean pleasant).
'e' inserted inside 'nice' is 'NIECE'.
(Other definitions for niece that I've seen before include "Female family member" , "A sibling's child" , "Young female relative" , "Brother's girl" , "Family relation" .)