@Loksel, isn't Sera like, already being implied that, she knows Conan is Shinichi? It was at the chapter where her mother who is "childized" assumed the Sleeping Kogoro's role instead of Conan if i remember right, the mother herself confirms that Shinichi is also in a same predicament as her.
Actually, now that i think more about it, maybe the more accurate reason for this Sera's behavior is because she knows that occasionally, Conan CAN reverts into Shinichi (she met him in person during that "School Trip" arc), and was wondering if she can also get a hand on whatever it is making that possible for her mother's sake.