In particular, I'd say if you look closely at Sagume's dialogue, you can see she's pretty specific about only reversing the situation regarding the relocation plan. (It's a little ambiguous, but she never talks about the invasion of the capital with any explicit details and talks about it only in the context of the relocation plan, so I'm guessing that's all right.)
So I think before the player shows up, Sagume knows that the relocation plan will definitely succeed, but she's not completely sure about how the capital invasion is going.
After the player shows up, Sagume speaks and makes it so that the relocation plan will definitely fail. She's still not sure about the capital invasion, but that's where the player comes in: Sagume is betting that her relocation plan fails as a result of the player stopping the capital invasion. (I guess this implies that there was the possibility of the relocation plan failing while the capital invasion succeeded.)