It is probably best you consider it was possibility a).
It is possible that your W looked at the clock and noticing the time, thought about you as it would be the "normal" time you would have picked your S up and then realized she did not know what time you would be picking him up in the morning, since she had not discussed it with you. If you want, an admission by her that she did not discuss a change in plans with you, even though she somehow created a memory that she did.
