With UK models I think your wife would have to lean across to the driver's side door handle and operate the lock button fitted in the handle recess. This can be done whether the fob is in the car or not. The vertical buttons that pop up or down when the doors lock/unlock are solenoid operated and cannot be used manually. In other markets MB fit lock/unlock buttons in the passenger-side door handle recess which is obviously much more convenient. The only locking options in the car's Settings are for your fob to unlock all doors or just the driver's door. I have a 2016 220d Sport Premium+