I wouldn't necessarily block your left, I would just put her on leash, and work on switching sides while walking briskly
Hopefully I can explain this right,,what we do when working both sides,,start out on your left if that's where shes comfy, walk briskly and YOU turn INTO her and about face, she's going to end up on your right,,walk briskly, again turn into her and about face, she'll be on your left. to go to off leash, drop the leash and work it that way...agility is kinda like dancing, so keep the pace up, and keep changing sides and moving...
I think for her to 'move' to your right side, your going to have to back up, start on leash, and work it that way, vs offleash to begin with..make sense??