... she seems to have manually switched her light switch to sidelights only whenever she drives.
I suspect no-one’s told her the lights are automatic and she thinks she has to switch them on and off, but is getting it wrong (see below). When we first got a car with auto wipers several years ago, my wife insisted on continually switching them on and off manually, it took some time to get her to realise that she didn’t have to do that, it was just habit because she’d always done it that way.
I wonder how?
I was unaware we had sidelights.
If it’s like the Mk3, then the rotary switch on the end of the lighting stalk has several positions. It’s too easy to turn it just one click to the sidelight position and think you’ve turned the headlights on because the dashboard indication will tell you the lights are on. But you need to turn it to the second position to get the headlights.
Given that modern cars have DRLs I’m not sure of the point of sidelights, the only thing I can think of is that the taillights will come on with the sidelights. Do the DRLs go off and get replaced with less bright lights at the front when you manually switch the sidelights on?