That's certainly fair, if there's really no other choice... [She's not wild about it, but she also respects that it has to happen, sometimes.]
The Earth I am acquainted with had only a few heroes attempt to repulse the invading force, and unsuccessfully. It was a covert enough takeover that by the time it became clear what had happened, no one was left to truly oppose it.
It can easily be said that killing the invader would have been the better route.