I have heard a lot of stories like this in my country. Hindus also have various rational theories proving the existence of ghosts. Personally, I don't have any experience. It was your grandmother, without her physical body, who was the one. She did not show up again because you said goodbye, and she was satisfied.

Souls loiter in the place after death for a few days. Our culture has ceremonies and rituals to pacify them and send them away after 12 days.