My lawyer said it is against the law to sue insurance companies in Illinois, how can I know if this is true?

I am not happy with the settlement the insurance company is offering my family in the wrongful death case of my young sister. She was killed by a drunk boater and the responsible party's insurance company is offering an unsatisfactory amount of monetary compensation. Our family's lawyer said we are only able to sue the responsible party and not their insurance company as it is against the law in Illinois to sue insurance companies. How can I research that and find out if there are any loop holes, or if this information is even true? Thank you for you help!