Then I have succeeded in making you feel some of the doubt and mistrust Zoey is feeling right now (and being evil).
I lean more toward the side that some of Samantha's behavior was calculatingly manipulative and planned ahead and some was opportunistically manipulative and played by ear, but most of it was genuine. Of course, it being genuine might hurt Zoey even more, because as Zoey perceives it, it means her mom could have chosen to be the mom her son needed at any given time and chose not to until her kid finally because what she wanted and someone she could vicariously live through to an even greater degree.
But ambiguity and open interpretation are key design goals of this game, so don't take what I say as word of God. From the knowledge that readers have which Zach doesn't, it might be easier to see Samantha as a broken woman who is forcing herself to pull herself back together through will alone to help her child when they very, very desperately need that help, especially when she feels guilt for making their child need her so much more and her unusual kindness and openness is part of her way of apologizing. But it might also be seen as a failed and exceedingly manipulative mother desperately grabbing at a golden ticket to at least some semblance of not failing spectacularly when it came to the family life she wants more than anything (or living through her daughter), and her overenthusiasm and years of worsening mental health led to her being sloppy for once.
I will say that there was a lot of intentionality behind the framing of that visit to the Legally Distinct Build-A-Bear and turning what is seemingly an overdue mother-daughter bonding experience with genuinely touching moments into an extended metaphor of how Zoey feels like her own mother has spent two decades trying to make Zoey in her own image and is even doing that now, and the heavy tone of that insightful family drama and friction is meant to contrast with the somewhat childish naivety Zoey has about how her mother's daughter might get along with her better than her son ever did.