The answer is absolutely no. It's not ok to wear contact lenses for a 9 years old girl, what's worse, it's seriously bad for her eyes. As we all know, our organs, our body system, especially, our retina are not mature at all for a age of 9 years old. Wearing contact lenses goes against the proper growth of her retina. Besides, children always rub their eyes with their dirty hands, which will give a chance for bacteria to easily immerse into eyes while wearing contact lenses, It will cause infection to their eyes. All in all, it's better not wear contact lenses for a 9 years old girl in consideration of her healthy growth.Thanks for consulting.