Is it permissible for a fasting woman to press her thighs together against her vulva to reach climax without touching it with her hand, and does her fasting become void if she ejaculates in this way?

It is forbidden to press the thigh against the private parts to achieve ejaculation, both during Ramadan and outside of it. The fast is invalidated by the emission of semen. The fasting person must refrain from sexual urges, including masturbation, and should avoid anything that arouses desire.