I'm 26, I just got my first real "muscle car" a 70 340 Dart. But I went the same route when I was young. First was the /6 73 Valiant 4 door. Had disk brakes, had air, had power steering, had a GREAT running motor, had no power, HAD TO SELL IT. (I'd kill to have the damn thing still.) I was 18 and brilliant, so I picked up a 273 64-1/2 Barracuda. Had to see how fast it went, had to chase down import cars, had to hit a pot hole at 100 and bring the torsion bar through the passenger floor... Now clearly boys are different. We have a broken "off button." But in many cases I was very ginger with the car. IT'S THE ONE TIME YOU DO NOT RESPECT IT, that you get bitten. And After hitting the pot hole, popping the frame, and missing a telephone pole by less than a foot head on; many thoughts passed my mind.
1. You're an idiot.
2. This 40+ year old lap belt didn't do a damn thing.
3. Doesn't matter if you stand on them, manual brakes have TINY master cylinders.
4. WHY that steering wheel is made of wood... that would have impaled me.
5. Where the HELL did that telephone pole come from?
6. At least I beat that A-hole in the farting Jetta.
NOW, i'm not saying don't. But she needs to be 100% AWARE of the risks. She needs to know it WILL kill her if she does not respect it. Her chances in it depend on the scenario. Airbags help, but every accident is different. In a Hyundai Accent, hit head on by Dodge Ram 1500, they won't do ****. Cars are dangerous. Old cars are more dangerous. A lot of this depends on how well you know your daughter. But the rest depends on how well she acts in the moments you don't know about. It's a tough choice. But you'll know if she can handle it. BE HONEST. Not emotional. It's her life. She deserves to know what realistically could kill her. You have a picture that looks like your hunting together. "Open the action and show me; so no one gets shot." is no different than, "Stay under 75, and be cautious in the rain with the rear wheel drive, so you don't have the steering wheel go through your chest." It's tough to say, but you will be happy she knows the reality. This isn't something to sugarcoat. It's big kid time.
Good luck Sir