I was thinking along the lines of shadow puppets too, but I think you're absolutely right about her hands making a rabbit. Here's a picture I found that shows how to make a rabbit shadow puppet using two hands (the way it is made in the chapter is slightly different):
Considering that she's a childcare worker, the woman probably entertains children using shadow puppets with her hands. Luckily in this case, there is a man named Usagi (rabbit in japanese) who is possibly, if not likely, the murderer who killed her, so with little time left to live, the woman used shadow puppetry as her dying message. The culprit probably noticed this dying message and decided to separate her hands to throw off the police.
As for Shiho appearing, I wonder how she will manage to let the detective boys escape. They would wonder about Haibara's whereabouts and wouldn't dare to leave her behind, so what is her plan exactly? Furthermore, will she really show herself in front of Conan, Agasa, and most importantly, Sera? I have a feeling that she would have to disguise herself in some way or fashion until the effects of the drug wears out. Guess we'll have to see in the next chapter.