Friday went smashingly. Our friend Cassidy from down the street came over to watch Lucy for a bit; Lucy was winning and happy and perfectly fine for almost the whole time (we ended a bit early, because she was getting upset). Cassidy obviously had great baby skills and I felt completely confident with her overseeing my daughter. I thought, "Why have I waited so long to do this?"
Then yesterday I got Cassidy to come over again. Cassidy was as competent as ever, but Lucy was uninterested in hanging out with her. I went into the other room for a few minutes to lie down for a nap, and heard screams (screams!) after just getting comfortable. I jumped up and went out to the kitchen.
She hadn't fallen or anything. She was just upset. I nursed her until she got happy again, and thought, "Well, maybe she was just hungry."
Went into the other room. The screams started again after only three minutes.
It was sort of sad: I picked up Lucy, and she was happy. But if Cassidy so much as even touched her, Lucy started crying again. Wow.
So I think this hanging out thing is going to be slightly more of a gradual transition than I first imagined.