Mawkish girl takes nothing up (7)
I believe the answer is:
maudlin
'mawkish' is the definition.
('maudlin' can be a synonym of 'mawkish')
'girl takes nothing up' is the wordplay.
'girl takes' becomes 'maud' (I can't justify this - if you can you should believe this answer much more).
'nothing' becomes 'nil' ('nil' can be a synonym of 'nothing').
'up' says the letters should be written in reverse (in down clue: letters go upwards).
'nil' in reverse letter order is 'lin'.
'maud'+'lin'='MAUDLIN'
Can you help me to learn more?
(Other definitions for maudlin that I've seen before include "Weakly sentimental" , "Tearfully sentimental, probably drunk" , "Effusively or insincerely emotional" , "Foolishly tearful" , "Soppy, lachrymose" .)