I think FS7 is referring to the young witch that blessed the blankets. When her and her mother left and she saw Stacia and Declan hug and maybe kiss, can’t remember now, her face changed.
The description was very brief, and I assumed it was an elf under a potion of some kind, kind of like they used in Summer Reign, or a shapeshifter/ monster of some kind that hasn’t been introduced to the reader yet.