Damn. Another good story. Page 3 (printed page 144): the sudden change of expression is well handled. This mangaka can turn on a dime!
The motives of the ghosts are anyone's guess. I speculate that they did not have a full understanding of their situation after death. The woman did know Yukie's name; maybe she overheard it in life (she lived nearby) and got it mixed up with her other memories postmortem. Poor thing. As for Ms. Yukie, I think she just had an episode of excessive politeness -- being Japanese -- and went along, not wanting to offend a friendly and apparently harmless "former acquaintance" she could not "remember".