40 year old daughter with BPD signs and behavior

[GracieMichelle]

I’m brand new here.
I have a 40 year old daughter who has not been diagnosed with BPD. She has all of the signs of BPD and I have had professional therapy that is familiar and has helped me to understand it is likely based on all of her behavior.
She is a single mother with a 7 year old child who is on the autism spectrum and is non speaking. Her father, my husband, died of ALS when she was 14. It was very difficult. She was particularly close to him. I remarried someone who had lost his wife and in retrospect it was very hard for her as well. She and I had a pretty close relationship considering our different personalities until a few years ago when she started angrily lashing out at me  and her sister some, over many things about the past, etc. I have been an extremely devoted mom and now grandma. Bring a parent was a huge priority in my life. My older daughter has three children and we are all very close.
The very worst happened about a year and 1/2,ago when my younger daughter called and said that her son had written that my husband had abused her son and she recounted that he wrote this out about an incident when he was 21/2 or 3 when my husband was caring for him. We babysat a lot. She had been saying he communicated by writing and it was all inside.
His head and that was how he expressed. When I witnessed this it was very clear that he was not writing but she was, besides the fact that my husband is the last person who would do this. He loves her son, but my daughter has always been strange about it.
After that horrible accusation I managed to maintain an awkward relationship with this daughter and grandson by going and visiting along, seeking therapy to help me in talking with her, learning that this was not the true her and she was hurting deeply, and be very cautious.Some  visits it went okay and others she was in her angry, tense, accusatory place. A couple times I left abruptly. I have throughout affirmed my unconditional love for the two of them. For almost four months now I have not seen her or my grandson. My pain is sometimes unspeakable.
The last encounter I had with her, when I was leaving and  usually set the next date, it went downhill and something about
it all ‘sucks’ and how bad the year had been come up, she said, ‘but I’m  not the abuser, mom. And I lost my discipline and said , ‘oh yes you are, yes you are’  
She has not returned my requests for another date to visit and a recent more fervent request to come and see my grandson.
In many ways this has felt harder than the terminal illness of my husband. That was catastrophic but it was black and white   I knew what to do, had tremendous support, and the answers were clear

I feel tormented with worry, pain, grief, and continual trying to figure out how to help her or say the things to get her to help. I have offered therapy together countless times. She refuses and says it’s all my people etc.
I’m hoping perhaps this is a place that can bring some  understanding for me, and some relief.

Our objective is to better understand the struggles our child faces and to learn the skills to improve our relationship and provide a supportive environment and also improve on our own emotional responses, attitudes and effectiveness as a family leaders