The girl would look and notice a large amount (8)
I believe the answer is:
shedload
'a large amount' is the definition.
'the girl would look and notice' is the wordplay.
'the girl' becomes 'she' (**).
'would' becomes 'd' (I've seen this in other clues).
'look' becomes 'lo'.
'and' says to put letters next to each other.
'notice' becomes 'ad'.
'she'+'d'+'lo'+'ad'='SHEDLOAD'
(Other definitions for shedload that I've seen before include "a lot of it" , "legion" , "great amount" , "Lots - old heads (anag)" , "a ton" .)