I hate to say, but there isn't much out there to get better fuel economy in a 4 door jeep short of tall skinny tires, maybe a rear axle swap to a higher gear, intake, exhaust and a fuel economy type chip may net you 2-3 miles per gallon. You have to factor that cost into how many miles must be logged to come out even and then ahead, which may be several years. So that being said, if she wants the Jeep, buy it, make it look nice and save the money for fuel instead of add ons in hopes of better mpg.