Ms. Cheerilee is the elementary school teacher for the Cutie Mark Crusaders and their class. She is friendly and patient, though can be stern when she needs to be.
She is single, and the Cutie Mark Crusaders felt that she should have a Very Special Somepony on Hearts and Hooves day, so they cooked up a love potion (that turned out to be a love POISON) and gave it to Cheerilee and Big Mac, hoping to get them to fall in love with one another. They did, but since the spell would have had them gazing into each other's eyes constantly, and ignoring their jobs, the Cutie Mark Crusaders had to correct their mistake by keeping the two ponies apart for 1 hour so the spell could be broken.
Cheerilee and Big Mac appreciated that the Cutie Mark Crusaders cared about their happiness, but punished them for trying to manipulate their feelings.
Call of the Cutie
Family Appreciation Day
Hearts and Hooves Day
The Cart Before the Ponies