In the end, Ves still hadn't completely figured Calabast out. She didn't fully explain her motives, which was regrettable because she was one of the few people in the clan who could fool his ability to read people.
As he grew older and came in touch with more formidable people, Ves became more proficient in figuring out people's true thoughts and motives. His ability to monitor the state of someone's mind and spirit was an especially great advantage.
However, Calabast was always able to withhold her true inclinations from him. Her impeccable training already gave her a good foundation, but lately she seemed to have focused a lot on suppressing the fluctuations of her mind. It was as if she knew exactly what Ves could do and developed her own countermeasure to make it harder for him to peer at her true thoughts.