My BC used to be the same way. Sounds like you are trying all the right things.
Some other ideas:
How are you teaching her to back up? I taught Mud by walking towards her with a treat over her head. When she was first learning it I actually had to walk right into her(not roughly, just kind of shuffled into her). At first I didn't care if she was backing up straight at all, just click and reward for one step backwards. Then click and reward for more steps backwards(and after that first time, I just had to step towards her and she would back up). When she understood she had to move backwards, then I moved to a hallway so if she backed off to one side, she ran into a wall. (This would NOT be a good idea for an insecure, fearful, or aggressive dog, because the small space might just make him/her feel cornered.)
As for pivoting, Mud has had a terribly hard time with that too. I started with a taller object rather than a shorter object. With a short object like a book or a piece of carpet, it's easy to step right off with their front feet. With a large object(like a bucket or a bowl upside down), moving their front feet means falling off of it. I clicked and rewarded at first for putting her front feet on the bucket. Then I stood on one side of her with a treat in hand. I used the treat as a lure and shuffled sideways into her. One step with a back foot, click and reward. I kept doing this until she would pivot with just me luring her around.
I also taught her to hike her back leg(What do boy dogs do?) by finding a ticklish spot(by accident) just inside one of her legs. I touched it and she'd pick up her leg--click and reward. She does it on cue now, but that's how I started it. I originally intended to teach her to lift each foot on cue but I just changed my mind.
Once she picks up pivoting, you can teach her to weave backwards through your legs and circle backwards around you.
Have you seen
Kikopup's vid on pivoting?
And also
Azoogle's vid on handstands(don't have to teach that now as if I remember right your girl is still pretty young??..but you can start some of it).
Since I'm still working on helping Mud find her back legs, not sure this is much help. :dogblush: Good luck and keep at it!