I doubt she was tricked, she probably agreed to work with Shikigami and then selected some/most of the people. That's useful wouldn't you say?
I've always read this as meaning that Shikigami convinced Mari to go ahead with the Swamp plan, and she agreed in part due to fear of Yagura but also because she honestly thought he could do better, and after that point Shikigami delegated the task of selecting the appropriate individuals and writing speeches, etc. so that the plan would succeed.
Mari is one of the people that when fall, they fall even harder because know what they are doing it's bad.
When she took revenge on her uncle, and broke all the taboos a ninja on her field have to maintain some boundary...
That was bad and it was even worse because she enjoyed it.
So we have a person without boundaries that feel horrible because she did some very horrible stuff, and feel even worse because she enjoyed doing that horrible stuff.
So how do you forget you're a monster? By going even deeper, because there isn't really much for you from your point of view.
So you have
Mari feel bad, but feel good too about it, so that means she bad inside, so she keep going bad things to ignore the problem(Because she's clearly rotten inside and can't do good,right?), so she feel bad.....ect.
Mari always wanted to do good, or, ironically, she would have never fallen so low, so when Shikigami told his plan, she went with it, even if other variables helped her.
It appealed to the part of her that wanted to do good, and felt bad and was just sick of it.
Mari is a self-described sadist. She enjoyed much of her work.
Meh.
To be fair, things like that have a certain, appeal to most primal parts of the brain, so it's not like Mari is intrinsically abnormal as she says.
But i think in Mari case what she
really craved was
1) Control, because she felt her own powerless when she was young and she never wants to feel that again.
2)A sort of punishment for herself: If she does bad things and she enjoy those, it shows to her she's rotten inside, so there isn't much she can go about it,right? So she uses those thing to drown the pain, because it's only thing she can do being a bad person, but that only make her even worse.
It helps with the pain, because it make her ignore the problem in the moment, on the other hand, it just make her feel worse, and so she then do even worse to forget it and reaffirm she's a monster.
At least in my humble opinion.