She has a lot of robot parts and fought with Thanos. The winter soldier was able to fight multiple humans and has an impressive metal arm. However he relies a lot on gun and he is still human.
She was able to survive longer than Tony Stark in space and would probably be more tougher than the winter solider and he would lose if he did not have any weapons.
Do you think one metal arm can be crushed by two metal arms? In theory yes but don't forget the Winter Soldier ripped up Black Widow, Falcon, And Captain so Nebula won't get it easy in a fight against the former Hydra servant but then she has her own def. Of machinery.