I would like you to see her paediatrician. Depending on the volume of the fluid in beakers, she should be producing normal fluid output in the absence of diarrhoea or other illness. Slight yellowing may indicate some jaundice, and I think it would be good to check out her kidney function too.
Excess thirst with excess urine output can be related to the diabetes mellitus, or diabetes insipidus disorders but dry nappies is not so readily identifiable in the absence of other causes of dehydration.
So I am sorry that I cannot be more specific, however a clinical examination will be able to identify the visual symptoms such as yellowing of skin, or eyes.
Regards
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