Without a complete assessment it is very difficult to give a diagnosis. However, regardless of whether it is ADHD or a behaviour problem, the behaviour needs to be addressed to keep her marks where they should be, instill a good work ethic and save sibling relationships.
At 9 tears old a reward system works very well, either a star chart or a record of behaviour with a reward at the end of the week etc. I would suggest you work with the school to show your daughter that you are all on the same page and she cannot manipulate the system.
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