Finding school boring and easy

Hi, we have come to the root of a problematic behaviour. Teachers (especially her senco) are amazing with my daughter and have found a pattern in behaviour. She is currently going through a phase (which happens regularly) which is constantly being bored and the work being to easy. 

She doesn't want to go to lessons any more (due to work being too easy or just being unmotivated or bored due to this). She likes to sit in the hall and chill out (which gets boring too) and she'll just constantly be wandering. We believe some of the behaviour she is copying from others in her class and in the school. The teachers are trying to see if they can get more challenging maths work in for her to do and earlier she managed to complete 2 GCSE Math Foundation papers in the space of an hour (she's Year 10). They did this to see how she would cope in a real exam and to see how good she is at maths. Unfortunately, her classroom has 3-4 other pupils in (another Year 10, a Year 8 and a Year 9) so they are all in different years so some would struggle more and some would find things easier. 

We don't know what to do because she's getting really bored and is close to walking out of the school grounds again. She is starting to sit on the gate which she can easily climb over and leave. She loves adrenaline so walking out of school and misbehaving (chucking chairs around or whatever) is giving her that adrenaline. But, being bored and not doing anything is starting to annoy her and she is starting to seek that adrenaline. Her brain needs to be stimulated all the time. I don't know what to do. Safety is starting to become an issue. School is trying but she just doesn't help herself. Any advice??? 

Thanks x