Good news!! This second garage said they will repair the car! (It only needs the glass as I thought all along)
I phoned them up this morning to ask about where the parts were coming from and they said Fiat so that’s also promising. I then brought up the issue of the frame that the glass sits on (because it’s only plastic) and they said if its damaged that too will be replaced so it should be good as new when finished (and hopefully it won't leak!). If all goes to plan the car should be fixed by the 4th or 5th of March so all in all I will have had to endure 2 weeks without a car. Although, I forgot to ask how much the final repair cost will be.
I also got a phone call back from the police, and the culprit will be interviewed on Saturday. They’ve spoken to his parents and the step-dad is willing to pay for the damage should he be found guilty (although I’m not sure his step-dad is fully aware of how much it will actually cost!).
I’m just glad things are moving (finally!) and I am getting some closure on what has been a very stressful ordeal. Furthermore, the engineer at direct line is to make a formal complaint against auto-glass over their handling of the situation.
Thanks to everyone on here for your support and advice