I just don’t understand my mom’s decline. Any thoughts?

Hello. I hope this is the right place to post this. My family and I are at a loss as to my mom’s rapid health decline. As of today doctors say she may just have days to live. This is mind boggling to me. Any insightful thoughts would be greatly appreciated. My mom is 70 years old. She has been smoking for about 55 years. Her mobility has been steadily declining for the past 8 years to the point where up to Dec. 11th of last year she was using a walker to get around (and she was getting around slowly). Other than knowledge of her mobility issues, all we knew about mom’s health was that she has severe arthritis. She has always refused to go to the doctors, until she was forced to on Dec. 11th. Here’s a timeline of events: 12/11- Mom is rushed to the emergency room because her oxygen level was at 74 and she was slipping into unconsciousness. There she was confirmed to have COPD (stage 3, I think). Diagnosed with heart failure. Additionally, she had all the symptoms of sepsis (although her doctor said she wasn’t clinically septic). Finally, she was diagnosed with pneumonia. 12/12-12/14: ICU where she was hooked up to a vent. 12/15-12/20: General floor. Pneumonia was cleared as well as septic state. Over the course of her 10 days, she recovered beautifully and was back to her old self (only now with the knowledge that she would have to deal with COPD). 12/21-1/21: At home. For the entirety of the month she is on 2L of oxygen at night and able to go without during the day. She also has physical therapy twice a week to help her get back to her walker. About two weeks in, Mom suffered a herniated disk in the lumbar region of her spine. Her PT was greatly impacted as the pain made movement difficult. An X-ray revealed the herniated disk and it revealed that Mom has severe degenerative disk disease. Anyway, by 1/18 Mom was clearly getting sick again. 1/21: Readmitted to ER and diagnosed with pneumonia. 1/22-2/24: Admitted to an extended care facility. During her stay there, she was never able to get back to 2L of O2. Over the month she would fluctuate from 15L to 4L. In the last week, she was mostly between 4 and 5L. Doc confirms pneumonia cleared about a week or so in. But mom was in great pain often so she ended up taking pain meds. These would essentially sedate her. Ultimately the pain often limited her PT. I should note that upon admission to this extended care she had two very small, mild abrasions on her butt. Anyway, she was ready to be discharged from the facility and her Doc suggested a skilled nursing facility to get her prepared to live independently again. By 2/23 (after a week or so of struggles finding a facility willing to admit our mom) we found one about 40 minutes away. 2/24: Admitted to new facility. Mom is generally quite sleepy for most of that first day. The next day she is sent back to ER because they suspect she has pneumonia, Again. 2/25-Now: ER and new extended care facility. Confirmed that Mom has pneumonia. Also, discovered an unstageable pressure sore on her tailbone. It is very disturbing to view and looked very infected. We were told nothing of this at her previous extended care. Her DOC thinks it may have happened on the 40 min ambulance ride to the skilled nursing facility. Anyway, for the past week or so, she has been on a vapotherm (generally 30LPM and 50%O2). They cultured the wound on her tailbone and discovered she has an acinetobacter infection, a very difficult bacteria to fight. She has been basically asleep the entire time (stirring occasionally to look at us and nod or give out the occasional one word response). They say she is just tired. What? Generally her vitals are fine. Today, they lowered the vapotherm to 20LPM and 50%O2. Simply put I don’t understand how my mom might die in days. Just a month and a half ago she was on 2L of O2 at night only and her old self. We were expecting to help mom live for years with COPD. And now she might die. Sorry for the long message and sorry if there are any errors in spelling/grammar (posted using my phone). We are at a loss. Any thoughts?