Oxygen how much?

Hi my mom sadly passed away yesterday after falling unconcious the previous morning.
I am wondering if being given 3ltrs of oxygen could have been the cause.
She had a chest infection from last friday (has had many and always bounced back) at 2am the nurse took her sats and they were 72.... (which again is nothing new after many chest infections)she has only had 1ltr oxygen in the past..has tank at home and c-pap at night...she was then put on 3ltrs and a 6am a nurse found her unresponsive,blood tests showed too much co2/carbon dioxide? In her blood ,then family were called to tell us she was going to pass away ,she fought for 24 hours .

She has had copd (end stage i think its called) for 15 years had a minor heart attack pneumonia many times, broken hip, covid
.
Can someone tell me if the amount of oxygen was the wrong amount as she was chatting just before it was given,from what ive read it is the wrong amount and can cause death