I know nothing about vintage frames/bikes, but I notice those topics get a lot of attention on this site. I'll have to do some reading.
I'm a little concerned about weight with vintage. But I totally see your point. She loves blue and she loves style.
I really don't see her trying a bunch of rides, but it might be worth exploring. Hopefully that would develop some buy in to the process. I just fear her getting burnt out. Maybe I'll narrow it down to 2-3 styles she likes and then set some dates to go visit specific shops with those styles.
I'm still hunting for suggestions or specific models people have liked after riding beach cruisers.