And maybe she turns out to be one? That could be possible.
However, I've seen season three at least twice through. I remember it well enough to know, at present, she's either; a) bipolar as **** or b) wanted Shane out of the way, but only as a defense against what he was capable of, meaning that she didn't necessarily want him murdered in cold blood. Those are the only two logical possibilities at the moment. Not saying the producers don't intend to turn her into a villain, but she's not at that point yet. One could argue the whole Shane thing is the gateway to such character, but whatever.
Anyway, not seeing how my point is that hard to grasp. There's a difference in what you guys are "implying" her intentions were and what she actually said, as well as the way she's acted throughout the season(s), thus far. Keep in mind, the rules change, at one point or another, in an environment like the one they are in, even if they yearn to be more civilized.
Besides, no one can really say that Shane wouldn't have had to be dealt with pretty soon anyway. Lori just happened to be the one to speak up, outside of Dale.
