In terms of women’s models that actually have different geometry to the unisex models, there isn’t much out there. It tends to be different colours, an offering in XS, different contact points, and hopefully a suspension tune for lighter riders out of the box. Cannondale, most Specialized models, Cube, etc. all update everything but the geo for their women’s range
The Canyon Neuron looks like it ticks most of your boxes, although standover on S size is 766mm. Looking around at other “women’s versions” I didn’t find many with an extremely low standover. The Specialized Camber (rrp is a little more than £1200) for example, has a standover of 728mm in Medium (which should match your wife at 5’6″). The Cannondale Habit is only marginally better at 722mm. The Lust has 719mm.
I am only 5’2″ and after starting on XS sized bikes (first a Specialized Safire, then a Pivot Mach 5.7), I up-sized last year to a Small size, as I wanted the extra stability as my skills and speed increased. I did a huge amount of research, and the first things I looked at were reach and standover. Here are two options worth investigating if standover is the first concern after price:
The Commencal TR V4 has a ridiculously low standover of 680 and is 1500 euro (without taxes).
The Radon Skeen 120 Lady 7.0 has 706mm stand over and is £1200 on bike-discount.de.
Good luck!