Welcome to just answer.
I am sorry to know about your daughter condition.
Now looking at her age,symptoms of dizziness which increases on head movement and nausea,there is a possibility that she might be having benign positional vertigo,which also presents with similar symptoms,ask the physician to do dix-halpike maneuver to rule it out.If confirmed ,it is treated with positional maneuvers.
Other possibility could low blood pressure
(hypotension) as you mentioned that blood pressure increases on standing,so ask your daughter`s physician to check her blood pressure on standing and sitting position.If there is fall of >20mmHg systolic blood pressure,you got your diagnosis.
Now other possibility could be undiagnosed ear infection which also may cause similar symptoms,and as you mentioned she does feel that her ear are stuffy so ask her physician to do ear examination to rule it out,as it is most common cause at this age.
Now looking at your daughters age,symptoms,malignancy is less likely thought it may also cause dizziness and vomiting but always better to rule it out by MRI brain,just to be on safe side.
Other possibility at this age,with no fever,no headache,no recent infection ,is less likely.
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