The actress, 33, was taken out of her comfort zone as Cassandra July, Rachel Berry's (Lea Michele) not-so-nice dance instructor.
"Being that mean for me, it's pretty difficult," Hudson told reporters on Wednesday at the Fox show's season 4 premiere at Paramount Studios in L.A. "It was challenging to keep a straight face."
Hudson's character seems to have it in for Rachel, who acts as a reminder of the dreams she hasn't already accomplished herself.
"I think she sees Rachel as this young, talented, cute girl, and she's just sort of bitten with jealousy and wants to make her life a bit miserable," Hudson says.
Despite the cattiness between the two characters on camera, Michele had nothing but kind words to say about Hudson in real life.
"She's the most down-to-earth, fun, laid-back person," Michele told PEOPLE. "I love working with her. She's just so spot-on and incredible."