My mother had surgery and was in an induced coma for a week, now her memory and perception is destroyed. Anyone experience this?

About a month and a half ago, my mom (seemly doing the best she has in years, despite chronic diseases, 74 years old) was rushed to the hospital for emergency surgery for a perforation in her abdomen. The surgery went well, but she was in a medically induced coma and didn't wake up for 7 days, extubated on day 8. She had trouble speaking, understandably. Once she could verbally communicate, she was doing okay, just occasional memory lapses, like why she was in a hospital in the city (which she's not), asking my dad When he was going to pick up her parents (who have been dead 25 years)..then when you correct her, she would say "yeah, I don't know why I asked that."...about 2 weeks later, we went for dinner and came back 2 hours later to her screaming at the nurses begging them to stop, my dad and I ran in, she told us to get out and never come back cuz we hadn't been to see her in months (we were just there that afternoon and everyday prior)..she's been that way to my dad in the past (recently her glucose dropped to 40 and in her state of mind she hit my father and doesn't remember any of it obviously), but always asks for me..next morning, didn't even remember any of that. She still has her feeding tube, but was transferred to inpatient rehab two days later to get her ready to come home--but she has been that way for about 2 1/2 weeks, increasingly worse than better most days, doctors saying it's a side effect of the coma and it'll ease up. This morning, we got a call from her rehab that she was being taken back to the hospital, her blood pressure plummeted and her "mental state diminished extensively"--when we got there, she was in a room, shaking and screaming at the top of her lungs like she was having a waking nightmare hallucination. Some of the things she said, my dad said are about events and people from her 20s and 30s, some even from her teens. About 5% of the time she knew who I was and asked what's going on and how me and the dogs and my fiancé are and cried cuz she was scared, the rest of it she thought I was her mother or a nurse. They're running tests to see what's going on, but my dad and I are fearing she's not going to come back from this. Does anybody have had an experience like this, or know anything about this? It's such a serious change in my mother (every time she's in the hospital, part of the things that I need to bring from home include her appointment book and her labelmaker...extremely meticulous and on the ball, even after a double stroke 2 years ago) ...but bc of her age, I fear nobody is taking it seriously.