Spoil that short girl (6)
I believe the answer is:
martha
'girl' is the definition.
'spoil that short' is the wordplay.
'spoil' becomes 'mar' (I've seen this before).
'short' means to remove the last letter.
'that' with its final letter taken off is 'tha'.
'mar'+'tha'='MARTHA'
(Other definitions for martha that I've seen before include "Lazarus's sister (Luke)" , "Sister of Lazarus; her Vineyard, Mass." , "Sister of Mary and Lazarus (New Testament)" , "Bible sister of Lazarus and Mary" , "- Jones, Doctor Who companion" .)