They will have to question any witnesses, the other students in this case and see what they say too. I doubt the teacher did it on purpose, but rather than saying it was an accident, she didn't intend to knock her down, it just happened, she denied it happening. More often than not the other students will be honest about what they saw unless they don't the student it happened to, or they don't like the teacher. I just read the first post to my students to see what they would say about it, they thought the teacher handled it very badly and shouldn't be blocking the door in the first place. She also needs to pay attention to which student she is taking papers from so she doesn't try and stop the wrong student. I'm watching to see what happens too, as educators we have to be responsible for our actions just the same as the students are.