WHOA!!!!
You are "should-ing" all over yourself. Second guessing is not a good way to go with this.
IF you had had this information ahead of time...(of course, you can't have, but...) COULD you have really changed your own life to try and change the outcome???? WHO gets to do that anyway???
When you were going through this and she was going through that, were you honestly saying, I can go be with my mom, I feel great and would do that, but I'd rather go to the movies instead??? HUH???? I doubt it.
You didn't willingly NOT be there 24/7 (and who can do that anyway?)
There is never a "good" time to die. Everyone's experience is different. You really don't know that if you HAD been able to change some things, that other things might have happened that still ended with her leaving.
Now stop it.

What you are putting on yourself is guilt, and guilt implies you DID something wrong. You didn't, imo.
Now realize that she isn't suffering any more, that she wouldn't want you to be feeling so bad, and put those papers away.
You are grieving. It's a tough process, but you'll get through it. (((hugs)))
I'm sorry for your loss.