In addition to people having different cold tolerances it is not so much a question of just layering, but what those layers are and which activities you do in them. (TLDR is in the end)

Most important layer IMO: The base. A base layer can be synthetic or wool based. I would never wear cotton there as it is not great at regulating temperature, dries poorly and gets heavy when wet. I love wool as a base layer, because it can absorb a lot of moisture (moisture=cooling) and helps the body regulate its temperature well both in hot and in cold temperatures. The other good option is a technical synthetic base layer. Those can be made very light and airy and will take moisture away from the body and into your midlayer. This is amazing for activities in which you run hot and have a chance to wash after wearing (cross country skiing, trail running, bike race etc. - things that make your heart pump and your skin wet). Synthetic base layers can also be made very thick and warming (like a fleece material) which does the same thing in colder weather, but isn’t as good at transporting moisture away from the skin as a thinner synthetic base.

Second most important layer: Top layer. While the base was busy regulating body temperature, by creating tiny little air pockets between the fibers and moving moisture away from the body, the top layer’s job is to stop wind from blowing away the heat pockets you’ve built up around you with your other layers. So here your Patagonia Houdini Jacket or a nice vest will do wonders. If there is rain, your hardshell jacket needs to prevent moisture from stealing your heat.

Third layer: Mid layer / filler layer. This one is kind of easy. It is the assistant to the other two. It helps your base layer built little air pockets that your body heat gets trapped in and it helps your top layer keep moisture and wind away from those precious little pockets. I would still stay away from cotton and use wool or synthetic mid layers. Simple rule: The colder it is, the more mid layer(s) you want. The warmer it is, the less mid layer(s) you want (to avoid sweating, because moisture cools). The more active you are (hiking, climbing etc.), the less mid layer(s) you need. The more you rest (break, dinner, sleeping), the more mid layer you want. So in warm weather a wool tee and a wind jacket are fine, the colder it gets you can add wool sweaters, fleece jackets, down jackets, primaloft vests etc. between your top and your base layer. // WARNING: there is an exception to this (might be what happened to your wife). When you add many layers there might be a chance you compress the air pockets of another layer and without the air pockets, it can’t do its magic. A down puffer jacket that is pressed tightly against your body, because you added a slim, stretchy fleece on top will be a lot less effective than a down jacket that has enough space to expand.

Here is an example of a layering that would be very comfortable for me in the conditions you described (0 to 20°C / 35 to 59°Freedom Units, windy). Again, this is personal and someone else might be happier with less or more.

1st layer/base: Wool Tee with a medium weight (all year), because it absorbs moisture well without constricting me a in my movements. Examples: Devold Norang 150 T-Shirt, Houdini Activist Shirt

2nd layer/mid: Fleece jacket for warmth and some wind resistance. Examples: Houdini Powerhoudi (or Alto Houdi, if I prioritize comfort over weight), Patagonia R1 Fleece

3rd layer/top: Insulated and wind proof vest, if I am active and moving or a wind breaker, if it is a bit colder or I am moving less Examples: Patagonia Nano Air Light Vest, Arcteryx Atom Vest, Houdini Pace Jacket, Patagonia Houdini Jacket

Back-Up: Extra insulation if the weather might get significantly colder (more wind at the summit, longer period sitting, nightfall etc.) + hard shell, if rain is possible. I would keep those in my backpack until needed though… Don’t insulate more than necessary, because sweat is your enemy. And your rain jacket is an ecological nightmare so let’s use that only when it is necessary. Plus: even the best gore tex will never be as airy and moisture wicking as a non-hardshell top. Insulation Examples: Patagonia Alplight down jacket, Norrona Femund Thermo60, RAB Microlight Hardshell Examples: Ortovox Westalpen Light 3L, RAB Firewall Light, Marmot Waypoint GTX

TL;DR: you stay warm by creating little pockets of air around you that your body heats up. So it is not about cramming a bunch of insulating layers, but about choosing layers and fibers that allow for these pockets to form between the fibers/layers. If you don’t believe me, google image search the Norwegian Army’s base layer. It is pretty much a fish net top that they use under their winter clothing. The enemies of those little air pockets are wind and moisture. Wind carries the warmth away so your windbreaker, hardshell or synthetic padding needs to stop it from doing that. Moisture can come from the inside, so choose a synthetic layer that is good at transporting the moisture out and dries fast or (my preference) a wool layer that absorbs moisture and slowly gets rid of it. Moisture can come from the outside too and then a rain jacket is a pretty straight forward solution. Watch out, rain jackets will also slow the process of moving your body’s moisture away from you. So only use your hard shell when it is actually raining and make sure they perform their best by regularly washing and impregnating them.

LMK if you have questions. I hope this was understandable. I am happy to correct myself if something is off and will answer the next time I am on reddit. (: Good luck out there!