@ericthesinner My girl is 6.5 and just entered this phase.
She has always been stubborn and willful.
Meltdowns seem to be related to emotional fatigue, like shes been at school all day processing interactions and behaving for the teacher.
When shes here (lives with mum most of the time) shes reverted to doing flips at the dinner table, refusing food, screaming and yelling and demanding attention, to be picked up, hitting when she doesnt get attention.
I'm calm and non reactive to most of it, and simply say no a lot. Hitting gets an instant stop and timeout (which is it's own battle)
We rough and tumble a lot, pillow fight and wrestle and tickle, so I'm constantly reminding her that this is ok when we're playing, but it isnt OK to hit people unexpectedly.
As soon as shes outside the house with other people it stops.
Theres 2 things I can see.... shes letting off steam or frustration from other interactions where she was unable to communicate or get her way.
2) shes pushing boundaries with mum and dad to see how far her own authority goes. I'm stricter around meals and manners than her mother. I think with time and patience it'll iron out but it's a hard phase.
Stick to your rules, allow her space to unload, make sure they get plenty of exercise, the phase will pass, and a new problem will rear its head.