I found myself initially in the same position as your mom. Well, not as a 48 year old woman, but as a 500 lb 30-year old man... both sedentary. Quite often, when we start to truly lose weight in a long time, we have issues with hips, ankles, knees, etc. Another concern (sorry for being "gross") is heavy people often have their inner thighs rub together, causing both pain and a potentially serious rash. If your mom feels like she will have issues with joint pain or rubbing, you can skip the walking.
In exchange for walking, try a stationary bike or a pool. At the speed your mom should be walking, she will be burning around 1,000 calories an hour. An hour on the stationary bike should produce about 1,500 caloric burn. An hour swimming slow, steady laps in a pool will find her burning 1,500 as well. If she can amp it up slightly, until she is slightly out of breath while swimming, she will be around 2,000 calories an hour. Swimming is great because it works many different muscle groups. While many would argue it's not a "core workout," I would argue that swimming is as good or better than walking.
Alternately, if you are looking for more indoor activities, do some research on "Turkish Get Up," a low impact core-heavy workout. Ignore the Kettlebells for your mom, she should be working at more flexibility and core strength than anything else. If she is over-weight and sedentary, she might have problems with "Threading the Needle," the part where your raise your hips to the sky and move the non-weight bearing leg. If that happens, have her focus on that part until she masters it.
Hope this helps,