Hello PCW. I join Bluek9 in welcoming you.
After reading your post I fully agree with whomever it was who advised you never to be alone with your grandchildren. Sadly, the warning flags are up.
I think most of us here, certainly me, recognize your daughter's erratic behaviour... .warm one minute then an about-turn the next. You no sooner get used to dealing with the current person she is, then broad-sided and scrambling on how to deal with the next. In reflecting, I really think I have suffered from a form of PTSD.
My heart goes out to you, PCW. When grandchildren are involved it can rip you apart. So glad to read that you do have other family, other grandchildren... .but... .always there is that hole in your heart.
You were upset enough to seek out this forum and I hope by participating on/in it you will start to feel a healing of sorts... .an acceptance of the situation that is the reality with your estranged daughter and tools (see to the right

|---> to mend and develop the relationship... .albeit, maybe, not the relationship you would like to have with her.
JustYouWait is one of the regulars here and I will quote something she wrote to another Newbie... .
"Welcome here. It is a fine place for people like us. In fact, the place is FULL of "us". We understand. Come early. Come often. Take what you need, and leave what you don't." Hope to hear more from you PCW as you document the journey you are taking with your challenging child. As well as this being a venue where you can let off steam and work on getting the strength needed to carry on, your posts are important for others to read.
Huat