The girl to gamble (3)
I believe the answer is:
bet
I believe this is a double definition.
'the girl' is the first definition.
'gamble' is the second definition.
(betting is a kind of gambling)
'to' is the link.
(Other definitions for bet that I've seen before include "Wager, back" , "Speculation" , "Wager, gamble" , "'Stake, wager (3)'" , "Wager, speculate" .)