A steadier ground guide to keeping the grandchildren connected to her without pretending it isn't hard for them too, at any age. What fear looks like differently in a six-year-old and a sixteen-year-old, what actually helps at each, and when their reaction needs more than a better conversation.
Notice your own urge to just keep them away rather than explain. That urge is protective and completely understandable, and it's worth a breath before it becomes the whole plan, since avoidance teaches a child its own kind of fear.
Before anything else: is the fear new, tied to one moment, or has it built gradually as she's changed? A child who was fine last month and is suddenly refusing to go inside probably witnessed or sensed something. A fear that's grown slowly is more likely about the accumulation of small unfamiliar moments than any one event.
Children read a room accurately and explain it wrong. They will notice that something is different, that the grown-ups are tense, that grandma doesn't act the way she used to, and without an explanation that fits their age, they'll build one themselves, and the one they build is often worse than the truth: that they did something wrong, that grandma doesn't love them anymore, or that whatever this is might happen to them or to their own parents next. Fear at this age doesn't always come out as words. It shows up as clinginess, as acting out right before a visit, as suddenly not wanting to be touched, or as questions that seem unrelated to the actual thing they're scared of.
Age changes what this looks like more than anything else here. A young child's fear tends to be literal and physical: not wanting to be in the room, not wanting to be touched, worrying it's contagious or that they somehow caused it. A teenager's version rarely looks like fear at all. It's more often quiet withdrawal, embarrassment in front of friends about a grandparent who acts differently now, or a flat refusal to visit that reads as indifference but usually isn't. Both are the same underlying thing, showing up in a body that processes it differently.
Prepare before the visit rather than managing the reaction during it, since most of what helps here happens before anyone walks in the door.
Note which things trigger the fear: a raised voice, not being recognized, a particular behavior, a particular room. Knowing the exact trigger lets you prepare for that one thing next time instead of bracing for everything.
Protecting a child's connection to her matters even when visits are imperfect, and a child's fear in this moment doesn't mean the relationship should end. It means this particular visit, or this particular approach, needs to change.
This is what the tracking is for. Knowing exactly what scared them and how long it lasted turns "the kids don't want to go" into something a counselor can actually work with.
A child who is scared right now can still love her, and still be glad, years from now, that you found a way to keep them connected instead of keeping them away.