Just guessing here. I'm thinking she is already reading much better than you realize...just silently. She's playing around by choosing random words on random pages out of boredom, or maybe a "game" she has made up in her own mind.
Look at it this way...I'm sure you can glance at a new book and glance at the first sentence and rattle it off while looking somewhere else, right? Because you already know the words, they are easily recalled. Same for her. She's reading the sentence quickly in her mind and then says it.
Try giving her the next two to three levels up in books. See how she does then.
