Look for other offer first... then either

1. can use as a trump card to nego for increment with current boss.

or

2. secure the way out.

Without other offers waiting on the table, ur cousin has no bargaining chip, solely at the mercy of the boss/mgmt. However, the mgmt will not take ur cousin's request lightly if they know ur cousin on the way out to other companies. Whatever it is, having options is the most sensible and best way to go..