Has she had an eye test recently?
How is her diet or sleep?
Presumably a problem with ear wax would have been picked up by doctor or ENT consultant? Equally, any sort of virus causing labyrinthytis? Or problems with eustachian tubes after swimming? Ditto iron deficiency?
Is she watching tv or screens before bed? Tablets or phones? Watching You Tube videos on small devices make me dizzy.
Or does she have a very windy drive or bus route home from school? There is a form of travel sickness that gives you delayed or continued dizziness.
How about anything she is drinking? Any fizzy drinks containing caffeine? Or medication?
If it is a faint sort of dizziness, could it be triggered when she is standing up too quickly to go to bed after sitting on the sofa? Could it be POTs for example?
Or, hate to say this, but assuming your bedrooms are upstairs, and she has just climbed the stairs when it is happening, could it be a cardiac issue? Presumably the gp would have picked this up if so? Or has she been over exerting herself at sport in any way?
Finally, is she happy at school? Is there anything going on there that she isn’t telling you about? Could it be stress of some sort?
I hope she feels better soon!