A pupil at Ysgol Dyffryn Aman in Ammanford, Carmarthenshire, as well as teachers Liz Hopkin and Fiona Elias, were transported to the hospital with stab wounds on 24 April.
The jury at Swansea Crown Court viewed bodycam footage of a police officer who arrested the girl and sat with her in a vehicle on the fourth day of the trial.
There, the girl referred to the pupil she had wounded, stating, "I stabbed her.
I apologise." Despite acknowledging the triple stabbing, the girl, who cannot be identified due to her age, denies attempted murder.