If my 16-year-old licensed driver is covered under her custodial parent's auto insurance must she also be covered under the noncustodial parent's insurance to drive the noncustodial parent's car?

This may vary based on your insurance carrier and the state you live in, but my insurance company told me I was unable to add my son to my policy if he lived with the other parent. If fact, the other parent refused to add him to their policy, and I was still unable to add him to mine because he did not "live" in my home. Our only alternative was to find a company which would set him up on his own policy, which I've been told is generally not allowed. Hope this helps.