My foot on the side that I broke my ankle on doesn't like to roll heel-to-toe either. Here's an exercise that my PT gave me that might help you too. It's called "retro walking". I walk slowly backwards, toe-to-heel, while I tighten the glute on the side that is currently stepping. He has me take relatively small, even steps with each foot. I do my retro walking back and forth down a long hall in my house for about 3 minutes each session and do 2-3 sessions a day. The retro walking is helping my foot to roll heel-to-toe again but I still have a ways to go with it.