Having a new baby changes the attention dynamics in the family. When each parent is emotionally mature, they can accept that a new baby requires a lot of attention. However, for your wife- your attention to the baby can feel like less for her. This isn't something to change- the baby is the one who needs care and you can't neglect the infant's needs- but it may be a contribution to the increase in your wife's BPD behavior.
Reading your post, I wonder if it's when you are holding the baby and attending to her that your wife "pushes your buttons"? Even if this is felt by you as a negative, it shifts your attention back to your wife. This is a reinforcer for the behavior to continue. If you don't react, she might escalate it.
I don't have advice on how to manage this but perhaps it gives you some insight to the situation. It may help to read about the Karpman triangle dynamics. https://www.bpdfamily.com/content/karpman-drama-triangle
From my own perspective, pwBPD are in victim position. The previous dynamic between you and your wife may have been you as rescuer, in an emotional caretaker position, and her as victim, receiving that emotional care. However for an infant, the actual need of care is real. The baby is completely dependent on adults for her well being, and yet to someone with BPD- your wife may be feeling the shift emotionally as you deliberately not attending to her.
Also, often the insults are projections of her own insecurities and more about her and you.You may be the more competent caretaker for the baby. While it's understandable you may be feeling resentful at having to carry more of the work of parenting- it's actually what your baby needs- it's for the baby. That may not make the load easier but may ease some of the resentment for you.




