Best wishes to your dd! I would be wanting an MRI.
I suspect she has a vascular compression especially given the appearance with certain neck movements. It happens in athletes when they over develop certain muscles on their throwing side. If this vascular dr doesn't get you the answer you need to find a sports medicine orthopedic surgeon that specifically works with people in throwing sports. Look for those that list among their credentials being a team doctor for a baseball pro team or college etc. Best of luck!
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