What I think is... MC is smart at last time to cut all the nuisance, but that is not a "smart move".
Now she know and has experience, she let them what they want, and show to the childern and society that, it is true in past life she made the decision to cut them all. Which when you think about it the MC will look ruthless and yeah bad, since the relatives hasn't doing anything yet.
I think she is collecting evidence, or maybe made the childern know that she actually protecting them by showing things that she cut down immeadietly in last life?
Like if you don't know about it, the childern will think the mc as antagonist like last life which MC doesn't want. MC decide to made smart move now, in last chap she know that they will try to made her as puppet and she will not yield to it.
First reason:
MC decide not to cut them off because the childern affection towards relative, which now in this life, they show they greed, and bad things about them, which made the twin realize, the aunt is bad after all.
Second reason:
She let it go because they seems like not much a big deal for her (now that she has all the experience from last life). Like even when things get bad, she can handle it.