Apologies for being a bit of a downer on this post but I just wanted to share a bit of my story.
My husband had BPD and is now recovered. It almost cost him his life.
Over many years, I was included in his intensive therapy. We had therapy sessions together and alone. His therapists believe that his mother also has BPD & NPD and concluded that her treatment of him, as early as a young toddler, was the reason why he contracted it himself (along with the fact his father has NPD). At age 6 he was already experiencing disassociation and age 10 he began self harming.
With this knowledge in hand as well as additional research into therapists that connect 'invalidating parenting' to the contraction of BPD, our therapists helped us to understand that the woman was poison around small children.
Worse thing was is that she believed that she raised her children well. Never researched her son's diagnosis and made any connections with herself. So last year when I was parenting her grandchild in her company she would dictate to me that I should be using her invalidating parenting techniques.
At this time we had never told her that we believed she had BPD or what our therapists had concluded (I'm sure you all know why - that some people just can not be told they have BPD), so throughout the year I was gritting my teeth to avoid any explosion (walking on eggshells) whilst deep down knowing full well her parenting techniques had been proven to be poisonous and even life threatening to young children.
All BPD sufferers are different and I note that LittleBlueTruck states that:
My mom is really great with them (I think)
So maybe LittleBlueTruck's mother is OK around little children, but it is well worth looking into 'Invalidating Parenting' (IP) and what many experts believe - in some cases they have found a connection between IP and children who contract BPD.
Not saying that all parents give their children BPD, as I am aware some children can contract it different ways, and some siblings may get it while others don't (genetically emotional children can apparently play a part). But in my husbands situation, his therapists held no doubt that IP as well as other dysfunctional parenting he was exposed to (ie simply being around irrational behaviour and arguments) that his parents were responsible for his contraction of BPD as well as his only sibling - his sister.
I am not saying that the children should be completely removed from their grandmother but if a BPD grandmother does portray IP and at times can think and act irrationally, then don't forget young children are learning everything in life including how to behave.
From experience, I believe the amount of exposure of the children (ie using a BPD grandmother instead of childcare whilst working) should be thought out carefully and possibly limited as well as other methods need to be put in place to ensure that the children know that "if grandmother says some silly things such as "stop being stupid"" for just being a regular 2 year old pulling off some pretty awesome dancing moves to music etc etc than the children should be told "that is just gran. You're allowed to be yourself and by the way your dancing moves are cool".