People can break their necks or crack their skulls on stairs - we weren't that fortunate.
No. People do not “run down stairs” (especially at her age and with her previous spasms and falls and numerous cases of “drug up the stairs” problems).
When they do “run down stairs” a person touchs the stair steps with the TOE of their shoes, slipper, or foot.
Because they are “running downstairs”, if their high heel “is caught” on some step, then the body’s momentum forces you further down the stairs, NEVER backwards. The toe then “might” be forced down into the next step, but the body is launched (dangerously!) down the rest of the steps at ever-increasing speed. But arms, hands, wrists, face and neck injuries are near-certain at her age and her agility..
If the body falls backwards, the toe is forced upwards, can’t touch anything, and CANNOT reasonably be broken unless both knees completely collapse and the body slides down the steps knees first, bottom back with the back and head sliding down and colliding with each subsequent step.