The bone plates had been installed, and the nerves were hooked up. Shou's recovery from that had been minimal, enough to surprise Winry and enough that she issued a warning to Simon, who was observing all this, that this was Not Normal.
So they'd gone ahead and installed the power source and port last night, but without the leg, nothing was activated.
Winry stepped into Shou's room to check on her. "How're you doing? Last night was kinda rough."