Magnolia Bennett's Links
Maggie met Cas through a series of unfortunate events during a class they share together (Maggie volunteered to escort Cass to the deputy principal's office when he was caught high at school, seeing as Cas was too stoned out of his mind to get there by himself). This awkward first meeting was what catapulted their friendship, and the two quickly grew close. Maggie supports Cas with all her decisions (even the terrible ones).
Cas is extremely grateful for her friendship with Maggie, if it wasn't for her Cas would be in detention every week for not completing homework on time (she got put in detention every week anyway, but not for not finishing homework on time). Obviously, that isn't the only reason Cas appreciated Maggie. Maggie's extremely kind hearted and accepting of Cas's decisions, which is something that doesn't happen often to Cas, which is something he's grateful for.