My niece asked me why women don’t ware a kippa? 1) I know that it is “more than just a minhag “ 2) Is it because that it is time bound? Please can you help me with the answer?

The reason women wear any head covering is as an act of modesty. The Rambam writes that even unmarried women should cover their hair, but most of the other Poskim write that only when women get married they are obliged to cover their hair. One should not make a mix up between the man head covering and the woman's. It is forbidden upon the woman to cover her hair as the man does (Lo Yilbash) and vise versa. The man covers his head as an act of Yirat Shamayim. Rabbi Yosef Weitzen