This poor social behaviour is actually a lot more common than I thought. I have known many people like this, in fact I had a co-worker who is similar to the one in your story.

*It was a furniture store, so big open space. No aisles or walls. Whenever it got busy, she'd always start walking around and around the place in a circle. Her walk is a stiff, quick pace and she would be looking dead-on straight ahead as she did this. I hated how she would practically walk right through the customers if they were standing in her path, without so much as looking at them. It was like she was in a trance. Weirdest shit ever.

*Even though it was apart of her job, she would ask others to answer the phone because she said she has a hard time talking over the phone. It wasn't a big deal either, because it was retail and people would usually only call to ask if we had a product, but I understood if someone who had difficulty with social stuff wouldn't want to. However, it was extremely annoying to whoever was working with her (usually it was two people on). She didn't seem to understand that if I was helping someone I couldn't be answering the phone also, especially if she's not doing anything and/or is standing behind the counter where the phone is located.

*Like you, she didn't know when to leave or when the conversation was over. I had to be the one who walked away or state very clearly I was going to go.

*Whenever someone spoke to her, she would look at them dead on in the eyes. If you moved over to do something, she would slowly turn her head following you. It was very robotic, I think that's the best way to describe it. Also gave me the creeps.