It's your hobby. Keep doing it.
Plus you're pretty good at it!
Don't see it as ignoring her wishes though.
The request is one of concern for you, which is not a bad thing. And afterall, Sunday illustrated pretty clearly that things can go wrong at the racetrack... but like you noted, as an Aussie male aged under 40, statistically you are more likely to die of cancer of heart disease than in a motorsport related incident.
My thoughts - fit a cage to the car.
Sure, it won't improve your times or make you magically impervious to 'when things go wrong' - but if you are to look at likely scenarios of a very bad day at the track, sliding sideways into kitty-litter and rolling would come up pretty high on the list. A cage could prove very helpful in such a circumstance.
Everything we do in life has an element of risk. That's what makes life exciting.
Most of the time we don't even think about it - I mean people choke on food, are you going to stop eating too?
Bottom line - if you feel unsafe, or that you might be risking too much, then stop.
Until that time, take all available precautions - and be a really cool dad that has a racecar!