This pranayam(breathing technique) will help increase the O2 level.It can be done in bed as well.
Build up your timing gradually.If you feel tired or dizzy, stop and resume after one minute.
Anulom Vilom –
Close your right nostril with thumb and deep breath-in through left nostril
then – close left nostril with two fingers and breath-out through right nostril
then -keeping the left nostril closed deep breath-in through right nostril
then - close your right nostril with thumb and breath-out through left nostril.
This is one cycle of anulom vilom.
Repeat this cycle for 10 to 30 minutes twice a day.
Children under 15 years – do 5 to 10 minutes twice a day.
You can do this before breakfast/lunch/dinner or before bedtime or in bed.Remember to take deep long breaths into the lungs.You can do this while sitting on floor or chair or lying in bed.
I'm certainly not a doctor, but your post did ring a bell with me. My mother took to her bed over 10 years ago when my father died. Nothing helped, and she is still in the bed. She can barely walk now, and she has had no life. While our situations are not identical, I do sympathize with you, and hope your mother will find the strength to start living again.
As far as her O2 levels... I have a lung disease, and my levels are very low. I am on oxygen at home and when I go out -- all the time -- to keep my levels up, and I have found that exercising helps. If you can get your mom to get out of bed, walk around and keep her on oxygen, I would think that should help, as long as there isn't another problem of which you are not aware.
Good luck!