Originally Posted by Acetylene

Either sit on a chair, like a desk chair or dining chair, or lie on a bench; then put her on top of you. That way her feet will be on the ground and she will not accidentally bounce you around and hurt you.

Also try having her bend over a piece of sturdy furniture, like a desk or dresser, then put a crutch under one arm and lean on the furniture with the other, and do her from behind. You should be able to triangulate between your good leg, your crutch, and your other arm. Should be possible but take it slow.