Re:
There is a lot of talk about specs, but not so much about the intended use your wife will make of the bike.
In my opinion, I would go with the modern bike, or even better a used modern bike (to get more specs for the same money).
Newer bikes, and specially the lower range you are targeting, have a more relaxed geometry, more comfortable than the long top tubes and even longer stems our retro bikes came with. As a general rule, at same height women have longer legs and shorter arms than men, just the opposite most retro bikes seem to be designed for.
My wife has a "modern" budget mtb at home ('07 Trek 3700), and then a decent retro mtb ('91 Scott WindRiver with full DX) by the in-laws (influenced by me) and she finds the modern one way more comfortable. In the retro, after her continuous complaints I had to raise the stem to the maximum, and when even at the limit was not good enough, we bought a ridiculously long quill/short reach stem which is both horrible and terribly comfortable for her.
The budget Trek, with its short top tube, high rise stem and high rise handlebar, was a success from the beginning. Heavy? Yes! Which one she prefers? The modern one in any case... We even do long tours with it. And she does not seem to mind the weight, as she has been "accessorizing" it with everything she finds: rear rack, bell, all kinds of reflectors, and clip-on mudguards with which she laughs at me when we come back from a wet off-road route and her back is still dry.
Your wife might prefer a racing low position, or prefers aggressive riding which a comfortable bike can't provide, who knows, so best is to set a budget and let her choose among the options available... A budget used modern bike and a good quality retro bike can come to a similar price (around 200 EUR). Also, female specific frames don't sell so much, so it's not hard to get a previous year model at a good price!