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The rolling back of the eye is called Enophthalmus and you read about conditions causing this on the following site:
Pain is a common cause for this to occur as is horner syndrome. Pain could be from corneal ulceration or injury which may be the case given the eye is discharging fluid.
Horner syndrome can also be a cause. You can read about this here:
If it doesn't occur at your house perhaps there is something at her house that is affecting the dog physically. Perhaps an allergy is leading to some inflammation of the eye and the allergen is not present at your house. Certain fumes might affect a dog as well.
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