I built Mama Murphy her chair when she requested it, and built it in a crappy little utility room in Sanctuary Hills. She took to it like she should, and was willing to trip out on chems for me.
I later built a cozier structure on top of that house, with a view of the wasteland, and moved Mama Murphy's chair to this location. Her "assignment" to the chair detached and she will not engage with it. Instead, she endlessly stands in front of the chair and complains about how nice it would be to sit down. I've even sat in the chair, in front of her, and spoken with her - not so much because I thought it'd help as I thought it would be mildly amusing. It was.
I tried relocating the chair a number of times to different locations, but she would not engage the chair in any of them.
I am unable to re-Assign her to the chair in the Build mode, as the NPC cannot be Assigned to anything.
If someone could tweak her script to periodically search for her chair and re-Assign to it, that'd be AWESOME.