Girl going by jet or prison van (5,5)
I believe the answer is:
black maria
'prison van' is the definition.
'black Maria' can be an answer for 'van' (black Maria is a kind of van). I'm not sure about the 'prison' bit.
'girl going by jet' is the wordplay.
'girl going' becomes 'maria' (I am not sure about this - if you are sure you should believe this answer much more).
'by' means one lot of letters go next to another.
'jet' becomes 'black' (similar in meaning).
'maria' after 'black' is 'BLACK MARIA'.
'or' is the link.
Can you help me to learn more?
(Other definitions for black maria that I've seen before include "Nick vehicle" , "Police prisoners' transport" , "vehicle for criminals" , "Old police van for transporting prisoners" , "Van with criminals" .)