^Indeed it's quite vague. The girl calls her Grandma we see in the first panels Obaa-chan (granny), and in the last panel the Grandma also uses "This senpai is your other Obaa-chan". To which the girl replies, "Really!? Obaa-chan was such a beauty, right?!", and the Grandma answers, "Now, ... also beautiful", referring to the same person the girl was calling beautiful. My guess is they are talking about the other granny :)