In the A&E "long Island Serial Killer" program there was an interview with Shannan Gilbert's driver Michael Pak.
In that interview it seems, IMO, that it was Michael Pak who talked to Joseph Brewer and made the arrangement.
And the fact that Shannan Gilbert didn´t know where she was at when she called 911, indeed indicate that it was Michael Pak that
made the arrengement with Joseph Brewer and NOT Shannan Gilbert.
After all, it WAS Michael Pak who drove the car that night and found his way to Joseph Brewer's house.
This is what Michael Pak said in the interview:
The Long Island Serial Killer. www.dore1.com - YouTube
Michael Pak interview at 2:33 :
" He (Joseph Brewer) said he was on Long Island, so I go; not so far...but then he offered 2 hours for 450$ and so, since there was no other appointments she (Shannan Gilbert) said ok lets go.
It took like a while to get there, it gets darker and darker, I was like; oh my God where are we going"
SO, IMO this indicate that is WAS Michael Pak who made the arrangement with Brewer and NOT Shannan Gilbert.