Another possibility is that it may be more to do with the attitude of one parent, and not specifically to do with neurodiversity in your grand daughter.
Our granddaughter stopped wanting to visit us with her parents in our house when her mother was very rude and negative about us to our grand daughter and our son, ie her father. This negativity can be very confusing for children.
I’ve noticed that if we go to their house, and her mother is out of the room or has gone shopping for example, that our grand daughter is her normal lovely self but when her mother comes back in the room, she’s very reticent again.
This parental attitude can be very confusing for children, and very damaging to some, especially if parents are verbally ghastly to each other.
We just carry on as usual, we keep giving birthday and Christmas gifts, and are hoping that this phase (mainly from her mother!) will blow over.
So sorry this is happening, but with kindness and also with realising that this happens to many grandparents, you will get through it.
🌷🌷🌷