Because I'd been able to get my leg across her back while standing on the rail the night before, I decided to climb the fence again and slip onto her that way. She was a lot more relaxed this time and stood still as I sat there scratching her neck.
I didn't try to make her walk anywhere. Just got off and led her to the center of the paddock. I tried again to mount her from the ground, and again she stepped away. This time I didn't give up, but gave it a second attempt, which ended up successful.
So ends the uneventful story of mounting up for the first time. I just love an uneventful ending, don't you?