I am praying for your mom! The same thing happened to my mother, not once but twice. The first time she was 29 years old. The aneurysm in her brain burst, and she was in a coma for weeks. This was back in the early 1960s. Brain surgery was not as advanced as it is now. To stop the bleeding, her surgeon tied off one of her vertebral arteries. There was a chance she'd be left with some brain damage, but the other vertebral artery grew to 3 times its normal size and took over the blood supply for the compromised artery. She recovered fully and went on to marry and have 4 kids.
The second time was 20 years ago. She started acting strangely on Christmas day, so my dad took her to the ER. It was another aneurysm that had not totally burst but had leaked blood into her brain. The blood leakage was causing mini strokes. When they did the dye test to locate the aneurysm, they found another one! They clipped both in surgery. Her energy level dropped after surgery, and she sometimes can't remember things that happened when we were growing up. Other than that, she recovered well. We are so lucky to still have her.
The brain is an amazing organ. Do not give up hope. I will pray that your mom recovers, and you have many more years with her.