Did Ash-Shafi'i permit wearing trousers, as stated in "Kitab al-Umm"?

Imam Al-Shafi'i, in his book "Al-Umm," stipulated that a woman wears trousers, socks, a head covering (khimar), and a dress (dir') during ihram. However, this does not mean he permitted wearing trousers without a covering, such as an abaya. Al-Shafi'i disliked a woman praying in a form-fitting dress and preferred that she only pray with a jilbab (outer garment) over it. Al-Nawawi mentioned that Al-Shafi'i explicitly stated that a woman should wear a thick jilbab. Trousers define and outline the body more than the disliked form-fitting dress (dir') and thin jilbab. Therefore, it is inconceivable that Al-Shafi'i would dislike what is form-fitting and then permit something that is even more so.