Hi David.
Your list of skis is pretty spot on. Of the boats you listed the Stellar SR would be the most unstable in rough water. It's more of a low intermediate / ambitious beginner boat rather than a real beginner boat. It's a really nice ski by all accounts if you can manage it in the conditions you intend to paddle in. The Epic V8 pro is another good looking ski in the beginner / intermediate category. The Nelo 520 is also a really nice little ski. I find it to be very stable although not quite as stable as it's 52 cm beam might suggest. I've never paddled a ski that accelerates faster.
It's the old story; try as many skis as you can. They all have a different fit and different behaviour on the water. What worked for me when I first started may or may not work for you. That FWIW was a Fenn Bluefin. It is a fantastic ski for learning to paddle downwind. Although I mostly paddle a Swordfish S now, I still take the Bluefin out on really big and/or rough days. My partner who isn't a regular paddler has no trouble paddling the Bluefin even in slightly choppy conditions.
Your wife would do well to try the Think Eze because that is a reasonably low volume ski as far as beginner boats go. At 60 kg she will float pretty high and get blown around a bit by the wind in most beginner boats. You might get a good deal on an Eze for her and an Ace for yourself.
Enjoy the search. Adam.
Current boats
Epic V10L Ultra, Epic V9 Ultra, Carbonology Sport Boost X LV, Fenn Bluefin, Nelo 510, Fenn XT double, Nelo 600, Expedition Kayaks Azure, Mirage 732.
Previous boats
Spirit PRS, Fenn Swordfish, Fenn XT, Fenn Swordfish S, Think Zen, Epic V10L Club, Carbonology Sport Boost LV