Maggie, possibly hard-boiled at heart (5)
I believe the answer is:
peggy
This clue might be a double definition.
'maggie' is the first definition.
Both the definition and answer are singular nouns.
Perhaps you can see a link between them that I don't see?
'hard-boiled at heart' is the second definition.
The definition suggests a singular noun which matches the answer.
'possibly' is the link.
Can you help me to learn more?
(Other definitions for peggy that I've seen before include "Dolly < bird" , "one associated with Sue" , "- - Lee, popular singer" .)