I knew I couldn't put it off any longer, so tonight I sucked it up and climbed on Gwen's back!!!
I took her into the ring so Coriander couldn't mug me but was right there on the other side of the fence. Then I stood on the mounting block and climbed up on her bareback.
Of course it wasn't quite as straightforward as that, but it was pretty close. I took it slow, starting by standing next to her shoulder on the block and rubbing her belly. The first time I swung a leg over she was a little worried about it and stepped away. But after that she stood like a stone. I sat on her back, clicked, got right back off and gave her a treat. I did that a few times and then finally gave her a treat while I was on her back. She didn't seem bothered at all about me leaning forward over her neck so she could reach it. She even took a few steps forward towards the fence quite calmly on her own while I was on her. I stayed up there long enough to give her treats from both sides and then I got off and put her up for the night.
PHEW! Giant hurdle #1 is out of the way! I'm not going to lie, I cried a little bit when I dismounted. Yup, I was that happy!