I would recommend Richard Simmons's SILVER FOXES video/dvd. Be sure to get the first one, not the one labeled "II" which doesn't have Richard Simmons. I think both are on the DVD. It's for seniors but would be easier for someone overweight to begin with.
Also, Amazon has these exercise recommendations for seniors:
http://www.amazon.com/BEST-Fitness-D...R3LIBEEZI78TVO
Even though your mom probably isn't a "senior," these would be easy for her to get started.
Walk Away the Pounds by Leslie Sansome is one that I've seen recommended a lot on 3FC also, but I've never tried it.
Jay