You could always simply ask her to please do some more research, and suggest good links/books (You know, the clear, simple, easy to assimilate kind. Not discussion forums, etc.) that have all the essential, indisputable facts, such as more surface area means more oxygen, grime gets caught in glass jewel substrate, bettas are carnivorous(ish), water changes per gallon.
"Well, I'd love to re-home my fish to you, but would you be willing to do a little reading on bettas first? ----- has a lot of important facts that every betta keeper should know"
Then, she'll make her own decision. If she still decides, "Hey, plant and vase are okay, then you still get to make your call. All keepers (just like all parents) have certain ideas of their own, but there are the indisputable facts, such as making your kid live in the broom closet under the stairs with no entertainment, exercise or engagement will lead to cuckoo brains