Toddler being aggressive to her younger sister.

Need suggestions on what to do. I’m getting so tired of my 3 year old being so aggressive to her younger sister. They are 15 months apart and she’s been so mean. Everyday she hits her, pulls her hair, bites, scratches, pushes her down, pinches and tries to put her body on her to squish her. If I tell her stop she’ll thinks it’s funny she’ll smile or laugh or sometimes cry and try to do it again. My cousin thinks I should pop her not hard but to scare her and I just don’t feel right doing it. I can’t even clean or cook because I’m constantly having to go grab my youngest away from her due to crying from my oldest hurting her. I also show them equal attention so I don’t think it’s jealousy or feeling left out.