Yes, I agree that if the landlord signed and exclusivity clause, them she has to deal with the landlord's broker.
However, this does not mean she needs to pay the broker because it is the landlord who must pay the broker. In other words, the landlord contracted the broker, not my friend. Therefore, she does not need to pay the broker anything.
The thing that is pissing me off is that she already paid the deposit and now the broker says that if she does not pay the $800 by the weekend, she will forfeit the down payment. I am really ready to let tis guy have it.