Why does my dog think a specific chair is evil?

Recently adopted a senior dog (she had been a breeding dog for 8 years- not treated well. she’s currently 11) and she is a bit skittish but is okay with people. We let her on any couch or chair that she wants. If she can’t reach it but wants up, we will pick her up and put her on it.

For some reason, anytime someone sits in a specific chair in the living room, she stares, then growls, and eventually it leads to barking at whoever is sitting in the chair. ONLY when someone is sitting there. She isn’t territorial (she’s maybe sat on it two or three times) about it, and she doesn’t want up either. We try to pick her up to put her on the chair and she backs away.

It’s becoming very difficult to have people in the living room because someone HAS to sit in the chair and she will bark and bark until the person is out of the chair.

What can we do?? What’s going on??