Too bad the story gives her absolutely nothing to do.
A bush on the edge of the clearing quivered. … Then, out of the shadows, a hooded figure came crawling across the ground like some stalking beast. Harry, Malfoy, and Fang stood transfixed. The cloaked figure reached the unicorn, lowered its head over the wound in the animal’s side, and began to drink its blood.
And here’s another passage from the final book of the series:
He got up off the floor, stretched and moved across to his desk. Hedwig made no movement as he began to flick through the newspapers, throwing them on to the rubbish pile one by one; the owl was asleep, or else faking; she was angry with Harry about the limited amount of time she was allowed out of her cage at the moment.
Which passage did you find more engaging? Chances are it was the first. While the second passage might advance the plot, the first passage has drama, tension, and irresistible vampire-like behavior stuffed into a matter of four lines. It’s the type of action that helps readers get lost in a book. And it’s precisely this ability to immerse readers that helps sell hundreds of millions of copies.