I was very lucky
My wife actually funded a good portion of our AT purchase...so no convincing needed.
Actually, I think the convincing started about 3 years ago. It was her first overland trip. I wasn't sure how she'd do without running water, toilet, etc. Back then, all I had was a ground tent and a shovel with a roll of TP. No RTT, no PETT, no privacy shelter, nothing but a great location, great plan, good hiking boots, a couple cameras, and great meals.
I planned the first night way out, all by ourselves. Just the wildlife, the mountains, and us. The second night I planned a stay in a bonafide campground so that she could use a real toilet, running water, etc. It was an unplanned convincer. There we were, stuck in the middle of a campground at Thanksgiving. 100's of people, dogs, screaming kids, tons of cars kicking up dust, wind blowing dust and ashes from nearby fires, radios blaring, etc. You get the idea. Plus, no privacy whatsoever.
Prior to that experience, she had always said that her dream would be to retire early and buy an RV and travel the country. Now she wants no part in that dream. She loves the private outdoors. Just us, a beautiful view, and the wildlife.
So, that's a really long way to get around to a small piece of advice. Would there be an opportunity for you to take her on two different types of trips. One in a state park or campground and one in the outback? Before you make the huge investment, could you rent or borrow one of each type and try them out?
My hope, for you, is that there will be little convincing needed and she'll come to a similar conclusion as you. If that doesn’t work, then the reliability and durability of an AT or KK would also be a good angle.
Regardless, good luck, and I'm glad you're in the financial position to make the leap.
TD