Sorry a girl's lost, that is (3)
I believe the answer is:
sad
'sorry a girl's lost that is' is the definition.
'sad' can be an answer for 'sorry' (I've seen this before). I am not sure about the remainder of the definition.
'sorry a girl's lost' is the wordplay.
'sorry' indicates anagramming the letters (letters in a sorry state).
'girl's' becomes 'ada's' (girl's name).
'lost' indicates named letters should be taken away.
'adas' with 'a' taken out is 'das'.
'das' with letters rearranged gives 'SAD'.
Can you help me to learn more?
(Other definitions for sad that I've seen before include "grey" , "Despondent" , "Dejected" , "Deplorable" , "Doleful" .)