I have considerable experience with some of this so I'll try to help.
First, I'm sorry to hear the terrible news. Thankfully she is alive.
Your medical questions cannot be answered here. You have only very broadly described her injuries and everyone heals differently. One thing in her favor is she is young (assuming from your post). Anything beyond that would be speculation. Bones heal. Instrumentation can be problematic over the long term and may or may not be permanent and/or require removal. Her pain will fade from it's peak now, that's just the process of healing. That does not rule out chronic pain in the future and it does not rule out a complete recovery.
Now to my area of expertise.
The auto insurance will not pay for your flights or expense.
It is the driver's fault. She is an innocent passenger. Assuming she was belted, she is 100% free from any negligence. If she was unbelted, depending on the state, the at-fault party could argue that her injuries would not have been as severe had she been belted. This would potentially reduce any award to her.
The driver is absolutely responsible. You have an absolute duty to maintain control of your vehicle. He did not. Start consulting with a lawyer. If the driver has the minimum state limits and no other insurance is available (UM, UIM) you may want to consider attempting recovery by yourselves rather than carve up a minimum policy with a third going to an attorney.
Or, you could try to negotiate a smaller fee depending on the limit available. The point I'm making is that based on her injuries and the clear liability, if the driver has a 25k liability limit for instance, the insurance carrier will happily write that check shortly once they get all the information and confirmation of your GFs injuries. That said, at least consult an attorney.
Oh, and again, it is his fault. There is no defense to what you described. And it's not personal, you're dealing with his insurance company.
Good luck and keep us posted as you get more information. I will be happy to respond.