Issues with school

Hi all again, sorry to keep bothering you but I feel so lost right now. 

My daughter has started getting a taxi to school, in the mornings she is fine, although she doesn't exactly like the driver because he doesn't talk much. Today was a bit of a negative day because she got out the taxi and as soon as she was on school site, she slammed the door shut. Her staff let her sit in the small sensory room, where she calmed down and completed all her work. Later on in the day, during lunch, she was bored and decided to do her math work, which she completed very quickly and finished 3 minutes into her lesson, she then was bored and did some PECS, ordered a lanyard and did some word searches. Unfortunately, she got too bored and left the room and sat in the nearest corridor, outside the sensory room and locked her staff out. 

They gave her space and then asked her if she wanted a staff change on a piece of paper but then she didn't reply and was drawing on the wall with the pen. Her favorite staff member, walked in hoping she could talk but instead my daughter tried kicking her then for safety reasons she had to be held. She didn't like this and was lashing out, kicking staff, biting, grabbing, pinching. While this was happening, she still had the pen lid in her mouth. Staff were aware but she wouldn't spit it out. She become too aggressive that staff had to release her and walk away with only 3 people watching her, where she then calmed down and had a chat and made the staff dance. 

I don't really know what to do next. Every time she has to get held, her behavior gets worse when they hold her. For example, she started off letting them hold her, then she was kicking, now she's not able to be controlled. But I don't know why this happened. Something triggered it but don't know what. School believe it was boredom but I don't know what to believe. 

What should I do next? If you have any advice, I really appreciate it. Thanks