My mother is on oxygen and while sitting it is 92. when she moves around it drops to 78. what would cause this'd?

Demand: Assuming the tracing is real and not movement artifact, the more you move the more oxygen your muscles and heart need and they use more of the available oxygen in your blood.

Hypoxia: Her lungs must be in pretty bad shape. Is she a smoker? If the oxygen saturation drops that much with movement she needs to tell her doctor and have her oxygen flue adjusted. Tell her to go to her doctor

Need more : Information but most causes of hypoxia are related to either heart or lung diseases. Definitely a full medical examination including tests is required