Hi Natalie,
I send my deepest wishes to you and your family for the loss of your mother. The photo of your mother is really nice.
It's hard to look back and wish you had taken photographs of the funeral because I am sure your sensitivity would have made the right photographic decisions. It's a hard decision and event to photograph but I don't think it's taboo, but rather outside the visual boundaries of most people. I have the utmost confidence that your photographs would have been special.
While you cannot go back, it seems that your mother is with you and I am glad that you got to spend the closing moments with your mother. The moment you described for the sunrise is really special and it's not a tragedy or a loss to photograph in this moment. At that moment in time she was beautiful and happy, and always your mother. You were trying to remember her as she was, a fighter and beatiful woman.
You should feel good that you STILL saw her as she still was, and that you took a picture of her that will last forever. Not with your camera, but with your eyes.
Again I am sorry for your loss.
Loren