A 17-year-old girl who violently attacked a boy over a sexually “inappropriate message” he sent to her sister risks being sent to Perth’s notorious juvenile detention facility if she continues to break the law, a Magistrate has warned. The girl was appearing in Rockingham Children’s Court where she pleaded guilty to the February 12 attack, which happened when the two sisters chanced across the boy while on their way to the train station. The court heard that the boy had previously made comments about her younger sister’s breasts in a message between the friends, which she thought was “really inappropriate”. When she realised who the boy was that day, the enraged girl attacked him. Police prosecutor Sen. Const. Gert Steenkamp told the court the 17-year-old first demanded that the boy hand over his Gucci bag. A fight broke out when he refused and she punched him multiple times to the face, before ripping two silver chains from around his neck. Legal aid lawyer Claire Rossi said the girl, who cannot be named due to her age, accepted that she threw the first punch and caused the escalating situation. “When she was told that this was the boy who had been messaging her sister she became enraged,” Ms Rossi said. “She and the victim exchanged punches, (but) he didn’t realise she was a girl until speaking with police.” She fled from the area but was later arrested and charged with two counts of aggravated robbery, one count of assault occasioning bodily harm, one count of damage, one count of aggravated burglary and commit a further offence, one count of stealing and one count of robbery. When interviewed by police the boy — who was bleeding from his face — said the girl had threatened to “shank” and “stab” him, Ms Rossi said. At the time of this incident, the girl was under a six-month intensive supervision order over a number of previous offences. Ms Rossi said however that the girl had stayed out of trouble since the February attack and that she had co-operated in full with police. Magistrate Catherine Crawford said: “Listen to me carefully ... you are doing well at the moment, but if you commit any new offences you could find yourself in very big trouble.” “Robbery offences like that will land you in Banksia Hill immediately,” Ms Crawford said. “The world is going to change drastically after your (18th) birthday and people will view you as an adult.” The teenager received a further six-month supervision order with program requirements.