Kari's experience in St Finbarr's Youth Arts led to her being part of the community cast in The Belgrade Theatre's production of The Wedding. Although Kari enjoyed acting, dancing became her main priority. It wasn't until she was doing her A-levels in French, Biology, and Drama & Theatre Studies that she realised that she wanted to pursue a career in acting. After leaving school, she moved to London to begin her course at drama school. In 2011 she graduated with a first class BA Honours degree in acting.
During the second term of her final year at Drama Centre London, Kari won the role of Lucy in The Inbetweeners Movie. She has since had various roles in a number of plays. She also appeared in the fourth series of the BBC Three supernatural drama series Being Human and the second series of Silk. She formerly appeared in the BBC Three sitcom Cuckoo, which premiered on 25 September 2012, as well as in The Musketeers, in which she portrayed Constance Bonacieux. In 2013, she played Danielle in the ITV comedy The Job Lot. In 2014, she reprised the role of Lucy in The Inbetweeners 2.