There are two reasons for this. One, if you expect her to come back, you have to make it worth her while. Second, these people work for minimum wage, the bulk of their income comes from tips. Just remember, the comps are free, the service must be compensated by you. Easy, join the slot club.
Every casino has a slot club or players club.
The casino looks on the players club as one of its major marketing efforts. The procedure for joining is simple. Just ask any employee where the player's club booth is. You will be issued a credit card sized players card in your name. Just ask for one, if the employee balks, tell them that you like to play two machines at once.