I've read some theories on a BBS dedicated to Fringe and someone put forth that Red could have been brainwashed by Walternate. Also, as to her so (apparently) easily committing murder, they put forth that she may come from a world that doesn't have the same morals that we have, or that she really believes she's in a war and is only acting as any soldier would do in the same situation. However, I go with the opinion that they have almost the same morals we do, since their universe is parallel and is (basically, with few differences) almost identical to ours.
With that in mind, that makes Red a murderer. Soldier or not, she chose to kill totally innocent people to get Peter on track with doing what Walternate wanted him to do. She could see for herself that Blueverse was not preparing for war, and while she expressed reluctance at killing innocent people, she still did it. She tried to tell Peter that while it started out as a mission that it ended up something more, but that didn't quite ring true, even if she was taking the photo booth pictures with her. She had a boyfriend on her side, why would she allow herself to fall for Peter? I'm more inclined to believe that she was taking home a trophy of her accomplishment at being able to fool the genius.
After all, the smug look on her face at the end of Entrada was more telling than anything. *Smug look.* "Like it never really happened."
Yeah, well, I guess the seduction never really happened either, did it Red? Are you even going to care if you find out that your boss was mutilated and sent over in your place to get you home?