Postcode to use for student

CliveOfIndia

Car_54 said:

You’re over-thinking this. 

Use the uni address, the four days at home are neither here nor there. Otherwise we’ll all have to tell our insurers every time we spend a night at friends, or a week at the seaside. And your daughter would have to tell them when she comes home at Christmas.

 All the insurers want is the “usual” place the car is kept.

This.  Certainly every time I've filled out an insurance application, it asks where the car is "usually" kept.  In your daughter's case, that's obviously her student accommodation.  And presumably she's putting her employment status as "student", so there can be no question of her lying on the application - insurers know that students will (in the main) be at home during holidays and such-like.

Even if something should happen to the car in the next few days, I strongly suspect the insurance company would have a hard time trying to wiggle out of paying on the basis that she'd lied on her application.