Really feel for you! Someone needs to get inside her head and work out what is going on. But how? Does she have a good relationship with anyone who she trusts and respect? Are there any psychologists in the area who have a reputation for treating ODD ?
Yes she has ADHD ,ODD and the trauma of a divorce; but is there anything else going on ? Bullying? sexual interference? etc Sometimes we get blinkered because we already have a multitude of explanations for behaviour patterns.
Lastly this is something you’ve walked in on, this is a responsibility that should be owned primarily by her mother and father. Just my opinion but your workload in this should definitely be less than 33 % of the total.
Kids with ODD have a real risk of transition to Conduct disorders At 9 this could be a matter of urgency and you can’t do this by yourself!
Although I am a retired GP I have no special expertise in this area nor an intimate understanding of this case so please treat my thoughts as just that.They could well be wide of thew mark, if so my apololgies