Thanks Charm and Sharon,

I will see if I can get my mother to not bite. She finds the idea impossible--if the device presses against the teeth, the teeth must press back, says she.

As for the flexibility, what you say strengthens my suspicions of a bad device. The upper mouthpiece is a white plastic arc that attaches to the blue main body through a narrow neck. In my device, this is how bendy the white part is--with the body held in my left hand, a moderate effort using my right thumb and index finger at the tips of the white arc bends it inward by over one centimetre (2/5").
Is that the same with your device?
The lower mouthpiece is one big white thing, and is relatively rigid.

The settings are correct, according to what you say (I'm an engineer, one may expect at least that much).

@Sharon
I got new bitepads from CranioMandibular Rehab, Inc. There was some problem with billing the order but everything cleared up eventually. Being in the US, you should have no issues. The replacement ones have their own gum.
As for external glue, Fevi Kwik works ok for us. Coming-off isn't the problem, in my case the pads get cut-through and ruined completely.

Thanks again!