Members of your household are typically all on the same insurance policy dumbass
as named drivers so the insurance company can assess the risk before your quote
You cant just let anyone in the house drive the fucking car and expect it to be insured.
What if your stepdaughter had multiple offences on her licence wouldnt that impact on your premiums?
If she took the car without your consent they wouldnt pay out for your car, they may cover any third party damage but Im pretty sure they woulkd looking to the police to prosecute your step daughter for TWOC
When you took your mums car without consent you were either a named driver so you could take the car anyway unless you mother called the cops on you
the other option is you were not a named driver and if you wreaked the car they wouldnt pay for it.