Forgive me for pointing this out, but when Mrs. Blue opened the door she would have seen one set of keys (hers) on the outside and a second set (yours) on the inside. I think seeing two sets of keys in the door would have most people thinking something was wrong and be extra cautious and figure out what was wrong i.e. that you had left your set of keys on the inside. Let's just assume that she is human and did notice that...and was able to figure out that you had left your keys on the inside.
I don't intend to make anything of this, but...I would ask myself why she didn't tell you about it. The fact that she left her keys on the outside while putting your keys on the table suggests that she was thinking of something other than completely correcting the odd situation. Since later she believed that it was her keys which she put on the table then I would suspect that the reason she didn't tell you was personal. On the otherhand she may have just had a more complex problem on her mind and you need to spend more time with her to help her through it.