Why did the house burn? If there is a person or company responsible for the fire, like a defective stove, they would also be responsible for the damage to your car. If your mom was responsible, her home owners liability insurance should indemnify her if a claim is bought against her for the damage to your car. They are probably denying the claim because it was made under the property damage portion of the policy and not the liability portion. Do you live with your mom? This may effect the policy coverage as well. You should speak to a lawyer in your area who handles property damage claims.
This does not create and attorney client relationship. As with all legal matters, you should contact an attorney in your jurisdiction who is familiar with the are of law in which you need assistance. You should make contact and seek advise as soon as possible as some claims have time limits and restrictions.
You should look at the homeowner's actual insurance policy (if she still has it). If not request a copy, and then look at it. Some policies may have a specific exclusion, some do not. The terms of the policy will determine whether the company has to cover it or not. Most of the time, they say the won't cover, even if they have to.
Jonathan S. Willett
A roundup of the best tips and legal advice.