Grim. I allowed my 16yo to stop contact with my ex's godawful mother about four or five years ago - having spent the previous time putting up with her unpleasantness for the sake of my kid who seemed to enjoy visits (but, looking back, was increasingly unsettled for a while after each visit). I initially tried, you know, talking to her about her behaviour as though she was a reasonable adult, but she just accused me of 'poisoning my grandchild against me!' (funny, as the years have gone on, my kid has occasionally mentioned more and more things grandma did that were an attempt to turn kid against me...) and refused (predictably enough) to accept that perhaps her own behaviour could have been less than perfect.
The real kicker was that when CPS (well, I'm not in the US, but our equivalent) got involved for a couple of years (kid was having some serious issues basically caused by being undiagnosed - thankfully that's now been set right - autistic and trying to navigate bullies at middle school and shitty behaviour from their father, compounded by my own disability making various stuff difficult, and unfortunately CPS, at least here, love to sieze on any disabled parent as Probably Neglectful And Maybe Abusive) they completely took grandma's side and said it was 'harmful' to my kid to, er, let them set boundaries (and back up those boundaries myself) about how much bullshit they were prepared to put up with from someone who happened to share some DNA.
Thankfully, in practice, they were too disorganised or whatever to get round to actually arranging the contact they wanted to force on us (and eventually I think the bitch's mask slipped a little and they realised maaaaaaaybe we weren't the ones in the wrong, though they never admitted it). She did show up (they did NOT warn us) to a meeting once, though, and started grabbing at my kid to try and force a hug, then whining when kid went statue-like before pulling away. Vile. The friend who came with me to the meeting (who is the sweetest, kindest person I know) said afterwards 'wow, she's a piece of work...'