Assuming grandmother is without physical disabilities, then she could
1) not sit for more than 30 minutes at a time
2) walk for 30 minutes moving her arms to increase the flow of blood
3) ride a bike
4) garden
5) household chores, like vacuuming, sweeping
6) walk on her tiptoes
If she's lying in bed she can do leg & arm lifts, rotate her wrists & ankles in a circular motion to increase blood flow.
Sitting for prolonged periods for anyone is not good. The arteries that feed your lower legs are bent at the hips and blood flow slows; puts one at risk for a blood clot.
