I like it and while Lynn was a "filler middle" name when I was growing up, I don't think of it as particularly dated. Probably because it was more common as a middle.  If I met a child named Leona Lynn, I'd probably wonder if it was a family name-which would be correct in your case.  It does make me think of Loretta Lynn, but it isn't an overwhelming association.

It does not sound too dated to me.  Leona sounds fresh and spunky these days--I really like it.  I can easily see it on both a sweet little girl and a grown woman.  Lynn sounds somewhat dated, but since it's a middle name I think it's more important that it be meaningful than just something fashionable.  Also, I think the whole name (first, middle, last) flows together really nicely.  I agree that Leona Lynn did also remind me a bit of Loretta Lynn, but I think that's a good association, so it wouldn't bother me, especially because she would be known more by Leona S----son than Leona Lynn, so it would rarely come up.  I like it!

I don't think it sounds too dated at all. Leona is one of the names I'm considering as a middle after my grandmother (Léoncia) as well, along with Leonie. Both are pretty and very usable, I think.

No, I actually think it sounds kind of fresh, like the other antique revivals... I'd probably categorize it with names like Fiona and Naomi. Lena, Lily, Lucy, Lana, etc., are all more popular now too, and Leona fits in with that group as well. I don't think it will feel out of place at all.

FYI, I have a student named Lourinda, and she seems to fit right in with all the other kids; I've never heard anyone comment on her name. There's so much diversity in names now, I think kids are just used to hearing a very wide variety.

That's a lovely, distinctive name with a great flow.  Excellent choice!