Are you doing any perch work/rear end awareness...once she's comfortable in her body and knows that it works, her confidence may come up. I use canned cheese to get my dog up on a peanut/balancing/turning/ sitting/platzing. Get a livestock feeder
and flip it upside down to do the perch work.
My dog feared a wobbleboard but after ramping him up while tugging and me banging it around while I was on it had him jumping on it and getting over his fear when it bounced/banged. His nails made noise on it too...which added to his sensitivity. Start small and work up, which it sounds like you are doing! You can see Karlo on the peanut in this thread:
Core conditioning training exercises
This is a fitpaws pillow which is way more than the livestock feeder, but works the same: