I’ve really only skimmed through this thread but it seems likely she has sensory processing issues. Many kids with SPD also have anxiety and being anxious tends to make the sensory stuff flare up. Ideally you can address her sensory needs in advance by having her swing, do big muscle work, doing activities that cross the midline should bring a reduction in odd movements. For sitting still there are inflatable discs she can sit on that give the sensation of movement. She can also stand on the disc to work on balance.
ETA loudness can also be a sensory issue. They don’t really notice how loud they are. Six years olds at their best are pretty emotionally dysregulated but adding untreated sensory issues to the mix makes it so much harder.
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