Questions

You make an explicit rule per the law... teen step daughter with temporary drivers license can only drive car you own/insure when another adult is in the car. It's the law in this state.

The rule is communicated and understood, but is violated. You give notice this is not allowed... don't do that again ever! Ok!

The rule is violated again a month later, under permission of your spouse whom gave permission. There was no emergency, just a desire to drive, and the teen driver asks (forgets or doesn't care) as well decides it's ok to violate the rule (oops)... and drives by themselves. "It's only a short distance" would be the justification. "It's not a big deal".

...

Probability of being caught by police or accident is small... driver has lots of experience and cautious. However, they are hormonally off (PMSing... and historically, judgement is off at this time) and there is a dangerous intersection involved in the well known, 1 mile drive home.

Severity of punishment resulting from an accident is substantial. You face cost or jail...

A) Insurance will fight coverage in case of accident... since the teen was violating the law, they can wiggle out of paying in court... cost shifts to the owner of the car (you) and parent... if teen was at fault.

B) If teen is at fault in an accident and death/multi party occurred, the responsibility shifts to owner of the car (you) and parent. Owner of car (you) could face prison time. I'm not a lawyer, it's my understanding of the law... and it's a liberal state.

What should a good, responsible spouse do in this case?

How do you handle your spouse that disobeyed the rule... putting you at risk you don't want?

How do you handle your step child?

Welcome to being an adult, and real life...