If your granddaughter was also driving without a license that's illegal too.
This one is pretty complex, because of the age of the people involved, and the laws where you are, but generally, your granddaughters parents might be held legally responsible, not your granddaughter, she's too young. When you break something you pay for it, no matter if permission was given.
No matter what the age is, although in the case of a minor, their parent or guardian can be held liable.
The drunken 23 year old can be arrested for distributing alcohol to minors, but that doesn't change the damage to the car, and who is responsible for it.
Its not silly at all, there can be many charges brought against several people involved, but that doesn't change the cost of repairs and who actually sent that car into the pole.
More than that, you have fifteen year old girl running around with a 23 year old drunk in a car and no one called home to say pick me up, or get me out of here. They were all lucky it wasn't worse than it was.