Reading fast is a good thing, it means that her brain can interpret symbols easily and can put a meaning to it. Its a gift which only few can get, but she needs to learn to concentrate, so i suggest that you promote her to read repetitively until she finely gets to understand the whole meaning in one reading. I know a girl who is around 15 years old and has such fast reading skills that she read The Lord of The Ring in 5 hours and was easily able to recall events and characters in the novel. It was really baffling, but its not just a gift but a lot of practices of reading faster and faster.