I just have to repeat what Julia said, good for you mom, how awesome is that that she is still so active at 83.
Leslie Sansone has a video titled Walk and Firm for Older Adults that might work for your mom. And Julia's so right about College Video, they are awesome.
Does your Mom live in a rural area or more urban? Can she walk at a Mall with a group of Mall Walkers or perhaps one of the hospitals in your area has an indoor walking program for seniors. Also, have you or your mom thought about Silver Sneakers? www.silversneakers.com/