Clear Mirror Dao Heart
She wasn't just naive, but she was also a bit simple-minded. Her thoughts weren't very nimble… at least that was Ryu's first impression.
It was impossible for a cultivator to be truly foolish. Even if one was born with below-average intelligence, much like beauty, it would only increase with time and qi absorbed.
Of course, it was possible that things were different with Nether Qi. Ryu had gained a large amount of it, and his understanding had deepened, but it wasn't to the point of saying that he understood it just as much as he did his Real Qi… which was funny considering he didn't think himself to be a great scholar of Real Qi either.
That said, there were methods of cultivation that Ryu knew that while they might increase the perfection of the body, did little to nothing for the brain. Those were rare forms of Body Cultivation, and they tended to also be extraordinarily powerful as well.