Assalamu alaykum
Women cannot shape their eyebrows. However, any unwanted facial hair can be removed as unsightly hair for a woman is not a thing of beauty.
The Prophet Sallallahu alayhi wasallam said:
Allah has cursed those women who modify their eyebrows or ask others to do it for them (Sahih al-Bukhari and Muslim).Hence, the reason for its prohibition is that it has been prohibited by Rasullallah (sallallahu alaihi wasallam).
