She was wearing a gown of satin.
繻子 (often spelled as 朱子) is a certain type of technique for textile fabrics. The fabrics made by 繻子 is called 繻子織 (しゅすおり).
繻子織 includes fabrics made of silk (i.e. “satin”) and of cotton (i.e. “sateen”), according to reliable encyclopedias.
Moreover, we hardly say 繻子 in Japanese. It should be replaced with サテン. It’s a common loanword.