Senior. In The Purple Piano Project, she was one of the students interviewed at the beginning and never said she was a junior, so she is a senior.
Also when Emma, Beiste and Artie told her and Rachel that they will doublecast the role of Maria, she said that she won't accept it, not in her 'senior year!' which means that she is a senior
AND she voted for senior class prezident. so shes a senior.