I think you are close to the answer. The family was attempting to arrange care for her during her trip due to the fact that she was disabled. Evidently the disability was not just that she was dependent upon a wheelchair.
A vendor who proposes to handle the disabled has a responsibility to understand the disability sufficiently to plan for success. This is what the family was expecting.
I would guess that any court case is going to hinge on whether the vendor was reasonable in letting the woman go on her own simply because the woman asked to. That is a foreseeable problem.
I can imagine such a vendor contracting to care for a seven-year-old. Would it be reasonable for the vendor to allow such a child to go on its own in a case like this? I don't think so.
How then did it happen that some employee thought it reasonable to allow this disabled lady to go on her own? The woman was an adult. The family had a responsibility to inform the vendor of the true extent of her disability and the vendor had a responsibility to act accordingly, even if that meant that the family needed to provide a custody agreement with the vendor or something similar to a "power of attorney".
It may turn out that several of the parties must share responsibility for what happened. Many accidents can be traced to a chain of failures.
All that would have been required from an attendant was to be cherry, interested willing to walk along side her to the next gate.
How was your flight?
Was the weather nice in Hawaii?
How are you off to visit? Oh, I have an Aunt Tilly too.
I think we might want to go the right here.
Perfect. Ah, I see Gate 23 up ahead.
We’ll get you checked in.
You get the idea. She could refuse my help, but could not get me to go away.