1) Because the UK car insurance market is irreparably broken, it's highly likely she won't be stopped. Why ? Because we have this ludicrous fiction of the car being insured, and then adding the twiddle of "the driver". So it's entirely possible that Daddys Mercedes sports car will sail past an ANPR check as insured, whilst little Johnny driving it, most certainly isn't. And until the law changes, that's the way it will stay.
We were surprised by this when we moved here. In america (at least where I lived), the car is insured, not the driver. The price of insurance usually depends on the primary driver, and any listed secondary drivers. Unless someone is a regular driver of the vehicle, they don't need to be listed, and anyone with a legal license is insured to drive the vehicle occasionally (convenient. if a friend visits, they can drive the vehicle for a few days).
I am sure one can easily see how this system I described can be abused. I can have a bad driving record and have trouble getting inexpensive insurance, so I will just get DP to insure the car. They do crack down on this (i.e. some insurers make it mandatory to list as secondary drivers all adults with a license living with you).
I don't know how it works in the other countries, but the system in the UK seems to be an odd mix of car is insured and so is the driver. also, it is inconvenient that others people can't drive your car occasionally.
I don't understand why anyone would think this is a good idea. Even if you think you're the best driver in the world there's always a risk of someone else crashing into you and then you're screwed.
I also don't get this. insurance is a very useful thing. if you invalidate it by doing something stupid, that could ruin you financially. Very odd thinking.