Roped in girl with reference work (7)
I believe the answer is:
'roped' is the definition.
(lassoing is a kind of roping)
'girl with reference work' is the wordplay.
'girl with' becomes 'lass' (I've seen this in other clues).
'reference work' becomes 'OED'.
'in' acts as a link.
(Other definitions for lassoed that I've seen before include "as stock is restricted" , "Caught with a rope" , "Roped livestock with a noose" .)