I would not really look at a diesel if her DD is just city. Stop and go, constant regens, your mileage would vary but this is not great for a diesel. If she has a solid mix of highway, then you could probably realize some savings. Those diesels, if I recall, use timing belts, they need DEF, fuel filters, the cost differential has really narrowed between them and gassers. I love my diesel 3500 but it is not an economic DD. On the open highway and with a trailer though, nothing will touch it.