Your DH is being a bit silly, unless your family history involves babies given up for adoption that nobody knew anything about, or secret marriages, etc.
Most really old people are happy to talk to a relative about family history.
I would send a letter first, with details of who exactly you are (include your maiden name, your parents' names and relevant grandparents' or even great grandparents' names, and any relevant maiden names too, and where they were born and lived). I would also include a photo of yourself, and copies of any photos of your parents and grandparents or older generations that could jog her memory and also assure her that you are not a dodgy chancer/Nigerian prince, out to rob her or swindle her.
If you arrange to visit, you might like to reassure her that you will not bring a carload of young children with you - sometimes older people get a bit stressed by children. Maybe arrange to meet her in a local hotel or restaurant, and buy her meal?
She might well be suspicious that you are interested in her estate and could interpret your interest in family history as an attempt to make sure you are her only potential heirs, so be prepared for a cold shoulder in response.