What is the ruling on a woman disguising herself in men's clothing and wearing a mustache or similar in order to participate in jihad, fleeing from the violation of her honor, and is this considered imitation, or does it invalidate her jihad and diminish her reward?

It is not permissible for a woman to imitate men unless there is an extreme necessity, such as fearing for her honor when being arrested. If disguising herself in men's clothes and appearance might save her, then there is no blame upon her due to necessity, and her reward will not be diminished. Allah Almighty said: "And He has detailed for you what He has forbidden to you, except what you are compelled to [eat or do]." Honor is one of the five necessities that permit committing a prohibited act to preserve it.