Bravery of girl soldier captured in Lowell's opening lines (9)
I believe the answer is:
gallantry
'bravery of girl' is the definition.
'gallantry' can be an answer for 'bravery' (gallantry is a kind of bravery). I'm unsure of the 'of girl' bit.
'soldier captured in lowell's opening lines' is the wordplay.
'soldier' becomes 'ant' (soldier is a type of ant).
'captured in' means one lot of letters goes inside another.
'lowell's opening' becomes 'gall' (I can't justify this - if you can you should believe this answer much more).
'lines' becomes 'ry' (abbreviation for railway).
'gall'+'ry'='gallry'
'ant' going inside 'gallry' is 'GALLANTRY'.
Can you help me to learn more?
(Other definitions for gallantry that I've seen before include "Valour" , "Overt courage" , "Courteousness" , "Chivalrous behaviour" , "Intrepidity" .)