Welcome to the forum dreama!
"I" haven't a "name" for it. I suppose there is one (seems names have been come up with for everything these days...lol)
But, I understand what she's seeing. When I lay down to sleep, I see images of people flashing, quickly in and out of my sight (minds eye) Full faces to small figures popping in and out, up and down, whatever...
If I lay there and "try" to see it, I can't
I've always just figured it was tapping into other times, spaces, realms or whatever. I've never tried to "figure" it out. Though I have said, "hummm?" to my self, and as soon as I do that, it's gone.
I've had similar audio experiences too. I'd hear hundreds of garbled voices some mornings when I'd wake and would go about my business. Like hundreds of people trying to all talk at once. Quite frankly I thought I was losing my mind for a little while. But, when I started to try and listen (to "figure it out or analyze it) it stopped. Well, that was one way to get it to stop I thought. So, that's what I would do when it started, because to be honest, I didn't want it to happen.
That was over 35 years ago now though...
I realize now that I was tapped into other realms or everyone's energy and hearing everything (everyone) at once...
Could just be that your grandmother is tapping into other realms
There will be others along shortly who might have other ideas as well...