Possible reasons why he can't go after her:
1. She has no assets, living on social security and living with a relative.
2. The courts have previously determined she is incompetent (dementia).
3. Her assets are placed in a type of retirement trust which is not assailable through legal action.
4. The Lotus, at the time of the accident was not registered (or insured) for use on the street. Many states make the accident automatically the fault of the non-registered car.
In case 1, you can sue, but with no assets, it is a waste of time.
In case 2, you can sue her caretaker, for failing to properly secure the car keys, if they have assets.
In case 3, you can sue, but the courts are unlikely to let you prevail.
In case 4, you can try to sue, but the courts are unlikely to let you prevail, you may face additional penalties on top of your injuries and loss.
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