Some suggestions from my experience with a partner who started riding with me, but remains a much more casual cyclist than I am. Here is one thing that worked really well for me and one thing I had trouble with:
What worked well: Choose with rides that involve a "fun" destination. I could go off and ride for hours in the middle of nowhere, but for her, it was more fun if she had somewhere to go. Typically this would involve biking 5-10 miles to brunch, or to the farmer's market. Gradually we could go to further destinations or add longer detours. Even after doing many longer (50-80 mile) rides with me, she's still more enthusiastic about "do you want to ride to dinner?" than "do you want to go for a ride?"
What I had trouble with: gauging the difficulty of certain rides for her. I didn't try to push her too hard or too fast, but occasionally I did anyway. While I didn't set out to take her on any big climbs, she had a lot of trouble with short-to-medium length climbs. These were the kind of climbs that might take me one to five minutes. Honestly, when planning routes, I often wouldn't even think of these as "climbs" because they were so short, but to her, they were often quite challenging. At her pace, a climb that would take me five minutes could turn into ten minutes, and she was less capable of powering over some of the steep stuff. These could turn what was supposed to be a fun ride for her into something rather unpleasant, and it took more than a few screw ups on my part before I learned.
I'll scrap the adventure ride to Mount Hotham - https://www.strava.com/local/au/melbour ... /routes/68
It's all about the adventure