I have only one child on the spectrum, so I have some idea of what you're going through. I've often thought that if, heaven forbid, I had to start dating again it would be nigh impossible to find someone who could cope with the restrictions brought on by SN parenting.
Anyway, I hear you in that she knew what she was getting into. And it sounds like she gave it a red hot go. But a mental understanding of the pressures placed on the family is different to the real life experience. When any of us attempt a new venture (in any part of life), we think about whether or not we could achieve the goal and if we think we can, we give it a go. However, thinking we can do something and actually being able to do that thing are very different.
I'm sorry I can't magic her into your life.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.