I am a natural blonde who dyed her hair red. It's fading pretty well, but parts of it are still a bit darker than the others. I was planning on letting it fade as much as possible before going to a stylist and asking them to try to match my natural color. But... I was wondering if I add a bit of 20 volume peroxide to my shampoo if that would help. I do not want to damage my hair, and if the results will just be streaky, I don't want to do that either. I just want to fade the left over color a bit faster.

Peroxide is very damaging to your hair, I'd leave that to the professionals if you feel the need.  But before going that route, I'd try oiling your hair to try to lift the color.