Lady's petition (3)
I believe the answer is:
sue
This clue is a double definition.
'lady's' is the first definition.
'petition' is the second definition.
(thesaurus)
(Other definitions for sue that I've seen before include "Take court action" , "The girl to take to court" , "Begin legal proceedings against" , "Entreat; girl's name (dim.)" , "Proceed legally against (someone)" .)