Let me just go on like I know what I'm talking about when really I'm making it all up.
I'm not sure a bent is any easier to balance than a regular bike. When I've been on rides and been near people on bents they often seem pretty wobbly, and appear to have difficulty getting rolling. It looks harder to me that a normal bike.
Why does she think she might fall? Is she generally comfortable on a bike, or is just balancing an issue?