I see a Chiari Malformation too, with her cerebellar tonsils (lower part of the hind brain) protruding though her foramen magnum (hole in the bottom of her skull) as indicated by the amount below the red line.
I see two other potential causes of your daughter’s symptoms also:-
1. She has a retroflexed odontoid (see the orange dot) this is where the C2, the peg bone near the top of the neck is bent backwards towards the brainstem. People can have this and have no symptoms but ……..
2. She MAY also have cranio-cervical instability (see the length of the green line, this distance seems greater than it usually is) but a series of other measurements would need to be carried out to be sure. Cranio-cervical instability allows abnormal movement at the cranio-cervical (head/neck) junction, which in people without Chiari may go unnoticed but, in those who have Chiari with their hindbrain herniated into this area, head movement and position can cause many problems, as subtle pressures are applied to this part of the hindbrain and subsequently the brainstem area.
The combination of the two (retroflexed odontoid and cranio-cervical instability) can cause a ‘pincer’ movement on the soft tissue of the herniated hind brain or the brainstem.
Has your daughter had a head or neck injury ?