You love wriggling in sister's grip (6)
I believe the answer is:
solver
'you' is the definition.
(the solver of this crossword puzzle!)
'love wriggling in sister's grip' is the wordplay.
'wriggling' indicates anagramming the letters.
'in' indicates putting letters inside.
'grip' means to remove the middle letters.
'sister' with its centre removed is 'sr'.
'love' is an anagram of 'olve'.
'olve' going within 'sr' is 'SOLVER'.
(Other definitions for solver that I've seen before include "Crossword completer" , "One succeeding with crossword" , "You're one, for instance" , "Private Eye" , "You find" .)