That is an oxygen concentrator, or generator. No tank involved.
MY f-i-l had one of those oxygen concentrators but also had a spare tank around just in case something happened to the machine.
Something is definitely weird about this.
They could have taken her to their house, notified the utility long ago that she was on oxygen, called 911, gone to a neighbors.
I agree with the suspicion that they are looking for a pay out.