My Girlfriend had a car crash. Now what?

She was hit by an air coach bus. By her recount of the story, it seems like he would be at fault. The guards were called to the scene.

The bus is fine but my girlfriend's car is destroyed. It looks like a write off. 2007 nissan Micra with a value of about 3k.

What's the best way out of this? Should we call the buses insurance and make a claim against them? Will that increase my girlfriend's insurance renewal? Should we wait for the guards to determine fault?