I am surprised that so many people dislike this name! It's not one of my favorites, but I like it. I've met one person named
Bethany, and I have good associations with it from that. I also like that it's not as common as
Elizabeth, and it's one of those names that to me sort of sounds like a nn but isn't. I like
Beth as a short form as well.
Overall, although I wouldn't use
Bethany myself (too many other names I like even more) I'd be delighted to see someone else use it. However, if you're set on trying to convince her to use something else (which obviously could run the risk of making her mad/annoyed), some alternatives that sound similar are
Annabeth,
Betony, and
Beverly.