A Perth high school girl who allegedly stabbed her teacher on Monday has been charged with plotting with another teenager to allegedly kill the educator. Police alleged the 14-year-old girl received a knife from a 13-year-old girl at Willetton Senior High School on Monday morning and used it to stab the teacher, a Year 8 coordinator in her 50s. The injured woman suffered a minor wound to her left armpit and was taken to Fiona Stanley Hospital for treatment. She was later discharged. The 14-year-old then fled the school grounds after the incident. But was later arrested by police in Willetton later the same day. The 13-year-old girl was taken into custody when officers arrived at the school. Police allege the teenage girls exchanged messages online for more than two weeks preceding the attack, which related to “talking about and planning to kill a teacher.” Both students were charged with attempting …