Legal Question in Insurance Law in Illinois

Insufficient information but you can try. First she would have to have her own liability insurance, not just insurance on her property, because you're seeking damages due to her liability (negligence). Since you don't say whether there were any official reports filed that state that she admitted causing the fire, you may not have any proof of her liability, the fire chief's memory may be questioned, and her admission may just be because she felt bad at the time. If the fire was something both you and she were responsible to avoid, her insurance company may raise the issue of "comparative negligence" and the responsibility is only 50/50 (even if she "caused" the fire), they may not cover it. Depending on how much you are talking about, it may be worth your while just seeing if she is willing to cover the cost difference, especially if all you're talking about is the deductible (if any).