I run winters all year and I drive far more than that.
They will wear faster but if she only drives a few thousand KM I don't see a problem.
There is a safety issue though, they will be horrible in the rain, and squirmy if it's really hot, an emergency stop situation can get hairy as the car will tend to squirm left to right rather than braking in a straight line.
I'm not sure if I would let my mom drive with winters in the summer, she wouldn't be as prepared as I am for funny things that might happen as a result of the soft tire.