I think she's thinking logically. From the perspective of a RelatRides lessor, fatal accidents are low probability events. That she experienced such an event yesterday doesn't change the probability that she'll experience such an event tomorrow. She's only naive if every single RelayRides lessor who reads this story is also naive to continue using the service.
She's naive because she's choosing to re-enter a partnership based exclusively on the perceived benefits (make money, save the world, etc.) without having a clear interpretation of the associated risks. Worse yet, she doesn't even have a clear answer on what her current liabilities are from her previous vehicle. I'm amazed her insurance company offers her a policy given her apparent disregard for liability she's potentially assuming on their behalf. I agree with your last sentence.
I think it would be prudent to not use the service until this is resolved in court. I already was worried enough before this to not use p2p car rental services, but this data point shows they carry inadequate insurance.