Could be multiple things, any other symptoms other than just the light coming on? If it comes on and she doesn't notice any differences in how the car drives, it could be anything from low oil pressure (BAD thing), engine knock (she might not notice the sound that comes with this problem) or just sensors stuffing up.
I know my HICAS light comes on a lot when driving back from Sydney, but I am 99% sure there is nothing wrong with it.
If neither of you know anything more than the fact that the light comes on occasionally, I'd recommend either taking it to somewhere like Trojan Motorsports in Mitchell, or Autotech in Hume....otherwise perhaps you should swap cars for a week and see what you think yourself, try to pick up symptoms when it happens. Stop the car and listen to the engine with the bonet up, immediately look at oil pressure, water temp, etc etc
Hope that helps a little, but unfortunately a little more info is needed like trying to diagnose what someone's illness is when all the can tell you is "it hurts here" and points to themself