What is the ruling on breaking a pledge not to shake hands with a woman who has wronged a female mujahid, if the reason for breaking the pledge is the fear of Allah?

A Muslim woman shaking hands with her Muslim sister is a religiously encouraged act. There is no obligation to fulfill a vow to abandon it, and no sin or expiation results from it. A Muslim must guard their tongue from indecent speech, especially declaring someone an infidel.