One sorry about daughter being less well-developed (5)
I believe the answer is:
ruder
'less well-developed' is the definition.
'one sorry about daughter' is the wordplay.
'one sorry' becomes 'ruer' (a person who rues).
'about' indicates putting letters inside.
'daughter' becomes 'd'.
'ruer' placed around 'd' is 'RUDER'.
'being' is the link.
(Other definitions for ruder that I've seen before include "More vulgar" , "Less mannerly" , "More impudent" , "Less civil" , "more robust" .)