Does anyone know the correct etiquette when it comes to use of the term Doctor and marriage.?

My father was a well respected scientist with a PhD, he remarried and died a few years ago. His second wife also an academic but only to Masters level not doctorate, now incorporates his title and his middle name into her name. So for example If my father's name was Dr. Ian Lloyd Smith she now calls herself Dr. Joan Lloyd Smith. It irks me to see but I wonder if this is acceptable use?