Let me see if I can clarify.
There is nothing in the law that is going to force them to pay anything if the policy had cancelled prior to her death. There is no law you can invoke that will require them to repay the premiums she paid while the policy was in force. There are no laws anywhere in the US that are going to make them pay a single penny unless the policy was up to date on the day of her death.
I understand that sounds harsh. I do not intend it to. The law is not warm and fuzzy. I am not trying to be cruel or unfeeling, but the law is not on your side here.
You don't get your auto insurance premiums back if you don't have an accident. You don't get your health insurance premiums back if you never have to go to the doctor or hospital. And you don't get your life insurance premiums back if you let the policy lapse a short time before your death.
Once again, I am not trying to be harsh or unfeeling. Really I'm not. I do understand that these are unusual circumstances here. But it's going to be entirely up to the insurance company whether they are going to look at those circumstances and make an exception for you. The law is not going to force them to do it. Anything they do is going to be a goodwill gesture. They are within their legal rights to say no.
You have my sympathies on your loss.