Q. Do women also kneel on Rosh Hashana and Yom Kipur?

A. Rivevos Efraim (3: 421: 2) quotes different opinions of contemporary Poskim, such as Responsa Shavit who maintains that women would do so in some congregations such as Frankfurt. Others assert that it is unnecessary or even improper. He also writes that when the Beis Hamikdash was extant, if women were to hear the holy name of Hashem from the mouth of the Cohen Gadol, they would be required to prostrate just as men were.
It is not uncommon today that some women in some shuln do kneel on Rosh Hashana and Yom Kipur. However Nitey Gavriel (Yom Hakipurim 57: 7) rules in regards to men prostrating, that all able people in a congregation should maintain a unified tradition. Otherwise, they may incur in the prohibition of Lo Tisgodedu, or separating into conflicting groups.
Horav Shlomo Miller’s Shlit”a opinion is that indeed all people should follow the minhag and customs of the location or the majority of the mispalelim.

Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit”a.