The transition from only child to big sister is not easy...
I was concerned that the experience might be difficult for Rebecca, so during my pregnancy, I spent time researching approaches for minimizing or soothing any feelings of resentment, jealousy or displacement.
I made sure that when we came home from the hospital, the new baby had a present for Rebecca, and that Rebecca's first view of me after several days absence was not one of me clutching a small usurper. The gift from Lucy worked almost too well - Rebecca was so thrilled to receive it, that she ignored Lucy completely. Over the next few days, she began to become curious, and at this point she is curious and affectionate. She gives Lucy lots of kisses and hugs, and is interested in watching her. One thing I didn't expect, was that Rebecca would find it very distressing to hear Lucy cry - she becomes concerned that Lucy is sad or that something is wrong - she tries to make Lucy happy again, and that empathy is very touching to see. Sometimes Rebecca herself will start crying or she will pretend to cry. At these times, I try to comfort her, and explain that crying is Lucy's only means of communication, and that for Lucy - crying can mean many different things. Hopefully, with enough repetition and exposure, Rebecca will come to understand this better.
We have seen a bit of reversion behaviour - Rebecca tried to sleep in the Moses basket, and also attempted to drink from Lucy's bottles, sit in her car seat, and climb into her stroller.
I think Rebecca missed us while we were in the hospital, but was so thrilled to be spending time with her grandparents, that she wasn't too terribly distraught. However, the fact that Lucy was with us to stay only really seemed to hit home one night when we sat down to supper and I was feeding Lucy at the table. Since then, there has been some weirdly contradictory behaviour - asking for one thing and then being angry to get it, and a lot of drama. Her normal extraversion seems to have switched to shyness - even with family members, so I guess she is feeling a bit insecure right now. Definitely, there have been more tears and more sobbing than is normal for Becca, and she needs extra hugs and attention.