What sort of moral trade-off are you prepared to accept in not reporting her ?
- that she may only hurt herself...........
- that she may only hurt herself and her passenger/s.......
- that she may only hurt pedestrians.........
- that she may only hurt pedestrians and herself.........
- and any other combinations.
Now factor in that ALL of the above, save your relative, are completely innocent, have loves, lives and dependents........how badly hurt or maimed is acceptable ?
If *dead* is pushing it a bit, then sodding well report her !!