Im sorry but I want to make sure I understand correctly. Everytime you try to pick up the canter, whether you are asking for the left lead OR right lead, you always get the right lead. Is that correct?
If that is the case, Raven is not listening to your right leg. Make sure she is listening to you and she moves off your leg... not pushing back onto your leg. I would bring it back down to basics. While walking keep asking her to move away from the pressure. If she is evading your leg at the walk she'll do it at the canter transition.
Get her walking in a nice rhythmic pace and ask her to move to the side a little at a time...off of both legs individually. Try to circle around only with you leg and very little steering. You will feel how responsive she is with your leg.
No hour of life is wasted that is spent in a saddle.
~ Winston Churchill