Why does the narrator say "She knew and did not know the things"? What does that mean ?

The narrator had gone back to see the things that had belonged to their family but were now in possession of Mrs Dorling. When she saw the things, she felt she knew the things well as they had been in their house for a long time. Yet she did not know the things because they were in new surroundings now. She did not feel familiar with them at all.