It's YOUR responsibility to make sure the car YOU are driving is legal, be it owned, leased, or borrowed.
You wouldn't drive a car with a flat tire, would you? Nice of the insurance company to offer to pay for the ticket, but if DUmmie boss had any brains, she'd checked for herself and point out the problem to the insurance company. Hell, I'm sure she's rented a car or 2 in her lifetime, where you INSPECT THE CAR YOURSELF and note any visible damage, because if you don't, you pay for it when you return it.
(We are talking about a DUmmie boss, so this could possibly be true.)