How do I get out of a car deal?!?

Yesterday me and my mom went to go test drive a Infiniti sedan G. The dealer pushed us into buying it because there were only two left. Since my mom didn't have the money to buy it right then, they made her keep a commitment to paying. She negotiated and got them to throw in the lifetime warranty window tint, lower the price a bit, and $500 off the 3M bra. Well, now looking back at it she knows she's wasting money because in the long run it's gonna cost her a lot of money, since the car is high maintenance. PLEASE HELP!