Though the big mac would be sufficient to get her to jump off i feel it wouldn't offer the motivation to get her on the roof in the first place, as it is only 508 calories. Consider things like a 4-pick of muffins, at 1600, or a load of chocolate bars selotaped together which could probably hit 4000 easily. At the very least, even with an elevator in the building, you;re looking at 3+ big macs.