Ch17 introduced Marcille as a magic research student interested in making dungeons and succeeded in their class experiment while everyone else failed was a hint of her knowledge. Not to mention her first reaction to when Farlyn showed her how she created her dungeon with all the elemental spirits around them was to forcefully create mandrakes to harness the magic to her whim.
It was already sketchy that she knew how to handle preserving corpses, preventing spirit possession and had utility protection spells when from what we saw, she was mainly using elemental magic. None of us was keen to catch that unfortunately...