Wow spaghetti! This sounds EXACTLY like my daughter. Even the crazy high reading fluency! How can you have such fast reading with such slow processing. I wish I understood more. And she was VERY bad 2nd, 3rd, and 4th, but now suddenly in 5th grade she seems to be improving, like you said and isn't even using extra time. And interesting that you had it rechecked and it remained the same. This gives me a lot of answers and confirms to me that I will just never understand this.
As far as the music goes, she tool group violin in 2nd grade and started up with school lessons in 4th grade. In second grade she played BEAUTIFULLY! Once she began reading notes it was all over. She couldn't do it and she didn't want to play anymore.
I don't know if it is due to slow processing or her tendency to flip symbols. I had her in ballet, thinking it would help the whole flipping and processing thing, but again, it was very hard for her.
She messes up her right and left and uses her left side to jump and turn. In ballet they start with the right side. All of this combined with the (fast for her) pace was a disaster. She has been doing a jazz class that she enjoys even if she is always a beat behind.
She likes swimming and is working on her strokes to join the swim team.
Her overall favorite thing in life it building things. She uses tape and cardboard and paper. I feel like if we could find just one thing she is really good at it would do wonders for her self esteem.
She WAS selected for a selective after school art program. She enjoys art, and is good at it, but doesn't seem to have the passion you need to sustain the interest long term.
I am looking for a robotics group for her..I think that might do it.

We thank you so much for your input. I will look into seeing if she would accept maybe private lessons for violin. Then they can go at her speed.