No decorrer do filme, aprendemos que:
Nebula got one of her limbs replaced by cybernetic implants from Thanos every time she had lost in a fight against Gamora.
Nebula: As a child, my father would have Gamora and me battle one another in training. Every time, my sister prevailed. My father would replace a piece of me with machinery, claiming he wanted me to be "her equal." But she won. Again, and again, and again, never once refraining.
At least one of her arms is replaced by such an implant. The implant enables her to destroy the ships. She is able to survive that because her implants allow her to take a lot of pain. This is best shown in the scene where multiple of her limps seem broken and she just snaps them back with ease.