It appears the two children had begun a heated argument in the school library between classes when the girl attacked the boy with a ‘sharp object.’
Given the assailant is a minor, she cannot be held criminally responsible for the attack. She has, however, at least been expelled from the school, or better said, a temporary expulsion.
The girl and the lad had been going out together until a week or so previously, apparently, and the attack was the result of jealousy on the part of the boy which, according to their school companions, he led to him bullying her.
(News: Vicálvaro, Madrid, Spain)