How you can do to make my daughter understand reading?

If you want to improve reading speed I suggest training to look at only two positions on each line (draw a thin, light pencil line one quarter the way from each side margin and only look at the place where that line crossed the line of text you are reading). Soon you should be able to read all the Words in the line without looking at more than two places on the printed line. You will then be able to increase the speed that you read each line. If you want to improve understanding of what you read then you probably will just have to read more and thus get a better understanding of the things you read about.