Catherine Merriweather is the Headmistress of Crown Lake Academy. She is also the aunt of Tiffany St. Martin. She is very strict about maintaining discipline and decorum at Crown Lake. She isn't very close too Tiffany, because she thinks she has become too sassy. She generally wears a long blue coat with a scarf and a brooch. She is the one who allows children to enroll at Crown Lake, and may also kick out students and fire teachers. She also introduces new students and staff, to the old ones. If the students are nice, she is nice to them in return. The Heather book which kids receive, prohibits them from speaking to her, unless she speaks to them.
While Merriweather may be too intimidating and strict, she ultimately takes decisions that are right for Crown Lake. She expelled Nick for drug dealing and fired Ms. Rose after Nellie exposes her. In the season 2 finale, she comes to speak personally to Tiffany after a long time, as Tiffany was leaving.
She has access to most of the school and is the only one that allows people to enter and exit Crown Lake, which are indications that she might be Heather. It is not confirmed that she's the real Heather Masterson.
This is a photograph of Ms Rose and Dana Roth as students along with two other girls. Ms Rose is the girl on the middle-right and Dana is the girl on the far right. Seeing as Headmistress Merriweather is a similar age to Ms Rose and Dana, some have speculated that the Headmistress may be the girl on the far left.
It is mentioned that her birthday is the 15th May.