It's fine. She scores a 3 out of 5 on the ass shaking scale.
What makes twerking/ass dancing 'work' is a combination of the size of the ass and the technique behind rotating it; which is usually dictated by dance experience and or rhythm familiarity.
So the larger the ass + the more advanced the movements are = higher score. This is why on average, black women score higher than non-black women. Genetics + rhythm familiarity -- as a result of Hip-hop, which is predominantly black music, being the foundation of twerking in North America -- give them a competitive advantage.
One of the pioneers of modern day twerking, Caramel Kitten, routinely scores a 5 out of 5. If you want to see her technique in action, her videos are up on YouTube. They're NSFW but she's fully clothed so you can watch it at home/in front of your friends.