Even in book 48 she came to the decision that taking Crayak's offer was bad all on her own.
I would certainly hope she would be able to easily decide that the evil creature that has plagued her and her friends since Animorphs 26: the Attack would not be one worth trusting
It's just sometimes they try to stress how much darker she was than the others, and imply that she wouldn't be able to cope after the war. I felt sorry for her because she was one of the strongest characters on the team. She would have been able to handle it.
I have to disagree there--on her being able to survive the war.
Rachel was opened to a whole new world, one she could never have conceived of before the war. Now, I'm not saying that Rachel would have had a meltdown once the war was over, but I think she would definitely be bored, or maybe even a tad upset that the war had ended at all--though, she probably would have hated herself for thinking that. But do you think Rachel could just go back to a normal life, pursuing a normal job--I personally pictured Rachel as becoming a lawyer, like her mom-- when she has done so much more? Even Marco seemed to get a little bored living his life of luxury, so who's to say that Rachel wouldn't have longed for the action of her Animorphs days?
Then again, maybe I'm wrong. Maybe Rachel would have managed to adjust perfectly. I just think that, given how Jake, Marco, Cassie, and Tobias never really maintained what you'd call a normal life, it's fair to say that Rachel couldn't either.