We all knew she was going to do this, but I personally thought it was done really well. None of this "undo everything" nonsense. Just 1 minute - and that was enough to change the outcome of the war.
The reason why she was only able to move time back 1 minute was probably because she had to give up a minute of her life for every minute she gave to everyone else. In other words, 1 minute times the population of the world/universe was used up.
I'm a bit disappointed that she died ('cause she was super hot), but it's too convenient for her to come back alive. Time reversal of 1 minute is okay, but I hope the author doesn't cheapen the sacrifice.