Just lodge the police report first. If your relatives have captured some scene photos during accident, show to the sergeant on duty.

Accident inside a basement can be really confusing but I have customers who have such issue before. They able to claim the insurance.
If your relative very certain she/he is not at fault, any scene photos will be great support evidence.

She's at fault, kena summon, claim against own insurance company.
Even in basement car park, there is priority lane too. Who to give way, etc