Maybe she has hated it for years.

Now we know why you're stuck having dinner with grandma rather than on a date. Get a better haircut, or better yet, a cool hat!

Maybe she only just noticed. Does she have new glasses or anything?

Senile people etc, tend to lose their "verbal filter" as the condition worsens. Would that apply in this case? :-( Or is she "merely" upset that she has no great-grandchildren from you perhaps yet? ;-)

maybe your grandmother is Evelyn Harper...

Simple. "You're one to talk" and then stop responding.