Help with right handed horse?

I bought a new horse 5 weeks ago, and we have been working together slowly. She is 8 yrs old, previously used for trail and school (very young and old or handicap), is very laid back and has a lovely extended even walk and trot and now canter. I have a small indoor arena and while at times Laila can seem somewhat green, she suprises me with lateral moves upon request yesterday. She would not canter in our small arena, so I took her outdoors for a trail ride as we typcially do following schooling, and asked for a canter on the straight just to see what would happen. Well, she picked up the canter on the right lead, a nice extended even canter. It felt really uncomfortable for me (not bouncy or that I was unbalanced, just uncomfortable). I think but am not sure that it may be due to my knee replacemet (right knee) and overall imbalance (my left stirrup has grown 2" in 3 yrs). This is the first horse I have had that prefers the right lead to the left. Before I school with Laila again or ask her for a canter, does anyone have suggestions on how to improve myself so I am comfortable on the right lead with this less than acceptable artificial right peg leg otherwise known as a knee replacement, or is there a way to get my horse on the left lead cantering so that she is comfortable? I am not an advanced dressage or other rider, I trail and endurance ride. Just looking to mesh with my new horse so that we can canter on occassion and both be happy. Thank You