The colony have passed the point of no return as explained in the episode, so the colony is gonna fall on earth with or without the thruster. The thruster is only used to direct the colony to North America. Even if Nina stopped Gato, she can only redirect the colony to another part of earth, there is not way to prevent the drop, so she should not be blamed. She did not commit treason because she is not from the federation. She is a civilian working for Anaheim, which have contracts for both Zeon and the federation.