Fancy lace covering one girl (5)
I believe the answer is:
celia
'girl' is the definition.
'fancy lace covering one' is the wordplay.
'fancy' indicates anagramming the letters.
'covering' means one lot of letters goes inside another.
'one' becomes 'i' (Roman numeral).
'lace' with letters rearranged gives 'cela'.
'cela' placed around 'i' is 'CELIA'.
(Other definitions for celia that I've seen before include "Rosalind's cousin" , "Frederick's daughter" , "lady" , "Character in Tales from Shakespeare" , "Daughter to Frederick" .)