Is she terribly sore about being single? (5)
I believe the answer is:
rosie
'is she' is the definition.
'terribly sore about being single?' is the wordplay.
'terribly' is an anagram indicator.
'about' indicates putting letters inside.
'being single?' becomes 'i' (one).
'sore' with letters rearranged gives 'rose'.
'rose' enclosing 'i' is 'ROSIE'.
(Other definitions for rosie that I've seen before include "riveting woman in 40s?" , "Girl's name" , "Cider girl" , "It could be tea" , "literary drinking companion" .)