Like a 3/32 track ring AND a chain dog? The straight line should be running in the gear that will give her +-70 gear inches. She is planning to commute on that thing too, pavement all the way, and the hills getting there would not call for anything lower than 40 gear inches. Specially since she would be leaving her stuff at her office. The bike would be doubling as light tourer, climbing machine too. So weight is an issue.