My son (21yo) was like this at your daughter's age (his main diagnosis is dyslexia). His processing speed score in 9th grade was in the 1st percentile while his GAI was at the 99th percentile. His evaluator explained to me that it took him about twice as long to do the sorts of things that the test was testing as it would a person at the 50th percentile. His evaluator also said that things should get a lot better by the time he reached his late teens/early 20s, and they have.
In 9th grade, he used to take FOREVER to do anything school related. We ended up putting him in school midway through 10th grade and the school let him have double time for testing and a slew of other accommodations. He absolutely could not take notes, and the school would not allow him to use a LiveScribe pen because they didn't allow recording (I still think it's weird). So he just didn't take notes.
Then a year later he did DE at the CC. Again, double time on tests, and the use of a LiveScribe pen. He tried it a few times and, even though he is a technology whiz, he claimed it didn't work, so he stopped using it. But that experience somehow helped him learn to take notes. I think using a pen instead of a pencil helped.
He also sped a bit. At home, double time for tests was never enough. Now he was easily completing his tests at the CC testing center. By the time the ACT rolled around, and they wouldn't give him more than time and a half, he was able to finish with time to spare! This is the kid who in 9th grade did a practice ACT and took quadruple time! It would be interesting to see if his processing speed score has actually gone up since 9th grade.
Now he's a junior in college, and he sometimes doesn't even use his double time accommodation--he takes many exams with the rest of the class.
Two things that helped with speed over the years:
Developing fluency. We spent *years* having him read aloud every day for at least 30 minutes. Also, lots of math practice problems. And lots of typing practice (which he didn't mind since he liked to use the computer). He needed to do way more of everything to become fluent than a typically developing kid--and way, way more than a similarly gifted kid.
Getting out of the homeschool environment. At home, he had no motivation to learn how to work faster. At school, he learned various tricks (as we all do) that allowed him to speed up.
The only technology that has been useful is keyboarding. His college textbooks aren't available as audiobooks and listening would take as much time as reading.
Do fluency readings with her. Have her read aloud every single day working up to 30 minute stretches. Start with something below her reading level and gradually work up so that she is reading challenging material. Make sure you have her read textbooks as well as fiction.
Work on her keyboarding skills. Have her type everything.
Practice taking notes in real time. My son prefers to use a pen to take notes. I think it moves more easily on the paper. Derek Owens math classes are actually an excellent way to learn to take notes. He provides skeletal notes and writes in real time on the screen. The Teaching Company lectures are a terrible way to introduce note taking to kids--they move way too fast. I suspect that many other "polished" video lectures would have the same problem. You want to not have to stop to write things down, so a person lecturing and writing on a board (or screen) is best.
I hope something in here helps!