For someone that has also lived for a very long time she could see Firren as immature or foolish.
ETA: the wife has had a very long life and she has been alone for a lot of it, she now has found someone that legitimately loves her and wouldn’t trade that for the world, she probably can’t help but see Firren as a younger her or something.
I love Frieren too, but the author fanboying too much about Frieren is starting to get a lil annoying.
EDIT:
It's just NOT the time after what's currently happening to Haru.
Also ALL Frieren chapters in MangaDex got nuked. All of them. o7