Awe... she felt so comfortable and at ease she just let herself right in!! I had one do that when I was bringing in groceries when I lived in Bethlehem. He was a big black and white tom cat, very vocal, and he followed me in the back door, up the stairs and right into my apartment and slept on my bed for a while. He didn't take notice of the others there at the time, and eventually wanted to go back out. He was such a sweet boy! Did find out he was a stray, and then found him a home with a girl who lived downstairs in my building... she called him Gabby because he was so talkative, lol.

Hope your girl cat comes back for a visit!!