It is rare, but Muslim women are allowed to participate in Jihad as warriors and are called Mujahidah.

No one is forcing these women to wear niqab, these women just love God that much. Most Mujahideen are men.

Why do Muslims fight Jihad? It is not out of hate, it is out of love for God. To be a Mujahid is to be someone who loves God so much you will fight and die for Him.