Thanks everyone. The last few days have been back to the so eloquently put "nice, older and comfy lady." No interest in the mousie at all. So I have no idea what got into her that day - guess the mousie was just getting out of hand that day.

Yes, Barbara, you're right, I did spray her little house with Feliway, and she abandoned it after that. After a few weeks of "airing out" I put some dry catnip in the house, and it's now back as her favorite spot again. Whew! Thank goodness I didn't ruin it forever for her. She just adores that box and always goes running to it, scrapes her paws on the edge of the cardboard, then sits on her "front porch" and watches the household go by.