Sundering stuff established in the Q&A

[tokinokanatae]

And how is feeling sad the same as having "basically no issues", exactly? Is she callous or not?

Her emotions don't tie into her actions, so she doesn't have issues doing those things. She sees "feeling bad" as an acceptable price to pay as long as her actions lead to the end she desires. In that regard, no sacrifice of lives is too great as long as mankind, in one form or another, lives on.

Maybe I'm being too vague? Most normal people hesitate to do the sort of drastic actions Venat does--even Hermes has an obvious tipping point if you look at the report scene--with the suffering that ensues. Venat does not. That is callous. It doesn't matter how much she cries prettily as the Sundered stands over the dead body of their mother, because feeling that way will never stay her hand if she feels the cruelty she inflicts has a result that is worth it.

EDIT: As for her actions, RE: Emet-Selch, it's not like Venat is cruel for the sake of being cruel. She was dead and Emet-Selch's soul was half-faded. Offering a small kindness when it's within her power to do so and won't impact her larger design is not something out of character for her. We can see that in her escorting Minfilia's soul back to the Source, when it would have been just fine in the aetherial sea of the First.