My Husbands Ex

Hi, my situation is a litlle different, I lost my husband last year in a car accident and we had been together 15 years married 5. His ex wife whom he divorced in 1991 started using my husbands last name before her married name just after he passed, she has been remarried 11 years and never used my husbands name until his passing....is this legal we dont get along at all and she believes that her and my husband would be back together again someday, so I believe it is to hurt me....thanks for any input....alice