I think there are so many good perspectives here.
First off, as much as I hate to admit it, I did feel some warm-and-fuzzies watching her story. But then again, I am a mom. It is easy for me to project my feelings and wish those for other people. It doesn't redeem her, but it doesn't mean that some part of that joy isn't genuine (and, as an OB once joked to me, "pregnancy hormones are a crazy drug").
For me personally, seeing her stories and having feelings of happiness is less rooted in her kindness/goodness/sincerity and moreso rooted in my own. Feeling that is understandable, and having emotional exhaustion, being jaded, and not feeling that about her stories is also understandable.
I don't think that acknowledging the happy parts of a new life being born necessarily means that the other stuff is going to be given a free pass (not saying that that is the point y'all are making, just contributing my thoughts).
It would be much easier to identify narcissists/people with personality disorder if they weren't charismatic, or had some (albeit twisted) version of love they make others desire from them. So I don't doubt that there are some facets of her that are grounded in reality and compassion. However we know that they are ultimately warped and twisted by her own doing. It's why people like her achieve such a following despite problematic behavior.
My father-in-law is one such person (a therapist guiding me through navigating his messiness once postulated that he has personality disorder based on his messages to me and my husband). It would be much easier to ostracize people like that if they didn't have moments of genuine love (albeit displayed in an unhealthy way).
Personality disorder in particular is a tricky one because people that suffer from it truly cannot process information that contradicts their perception of reality. So it goes beyond an unwillingness to admit wrong, it is an incapability to perceive wrongdoing.
In Sarah's case, it is extremely harmful because (as so many people in this forum can testify) she has the power to influence others into a poor state of mental health or dangerous behaviors.
TL;DR It's normal to have compassion for a mother who just gave birth, and it is also normal to be unable to have those feelings in response to someone that we know drives others towards disordered thinking. Narcissists are tricky like that, they can trigger other people's genuine feelings of love.
Edit: "aren't" to "are"