Hey C.,
I don't know if you have tried this, but it may help. It was suggested to me for another issue I had. It was similar to this, so it may work.
This will take some time as far as research, but is so worth it in the end. You can do it one of two ways:
Get a notebook and notarize the visits. Get as detailed as you wish, but don't include thoughts, feelings, or assumptions. Only include what actually happened-Just the facts, Madam.-
Then after a few visits, take the notebook to the grandmother and explain to her that she is unknowingly affecting your son. You need her to sit down with you and go through your notes and explain to her what you see from the outside.
The Second suggestion is the best if you can do it. Get a video camera. Tape a few visits. If she asks what for, you can always play it off to keeping memories up to date. But after a few visits, again ask her to review the tapes with you and point out instances where she is neglecting your son. You can even keep a tally board on a sheet of paper so that she sees it is a reoccurring instance.
She may get a little offended, which is expected, but if she can not understand that you are doing this for the well being of your son, then I don't see why she should be around him anyways. Someone that doesn't care about what they are doing to a child, especially when the emotional harm is pointed out to them, shouldn't be influencing a child's life anyways.
That's my two points, and it did help when I brought it to the attention of another individual. There was a little tension, but after a few days of them thinking it through, they realized what I was talking about. Things are great now!!