I actually would expect a woman of 60 in this day and age to be a great deal more current. The days of identifying a woman as "Mrs Barry Bloggins" go back 30 years - and even then it was 60+ year olds that did that. Thus, I would expect only women in their late 80s and 90s to use that very old form of address.

Besides which, you are direct family, why would she feel the need to use such a formal manner in the first place?

I'm glad you are speaking up. I also would not dismiss this as a trivial matter. It cuts right to your very identity. It is also terribly rude not only hurtful.