Oh, I'm pretty sure it's a jealously thing. I've actually tried to get River to sleep in bed with me; she'll stay for a little while, but then leave. Which is odd, because she'll stay with me practically all day on the couch, even when we nap. She was a great companion when I had the flu She and the puppy get along fine now; they even play together.
I'm trying to figure out how to tell when she'll decide to be jealous. Like when my sister napped in my bed; I never would have suspected her to pee after that.
Yes, the puppy does get a little more attention than River, but River still gets her one-on-one time. In fact, learning to train a small breed puppy has helped me see where I made mistakes with River, and to correct them.