Fen and OPEN
Fen was probably not even sleeping all that much. Things have been quite dramatic recently. She was mostly just resting her eyes sitting by the water till she realized she wasn't allowed and then saw the mermaid.
She gasps slightly because Fillory probably has mermaids too and she knows the lore so she's about to step back a bit but she's already too close to the water and they manage to grab her. She's got a few daggers on her though (who is shocked) and she manages to injure enough to draw back slightly and yell out for help.