Is the discharge coming on its own or only when the nipples or breasts are squeezed? Some discharge is common in women on breast squeezing and a nipple discharge is significant if it comes on its own, is bloody or foul smelling, associated with skin changes, lump etc.
In any case, you should ask the doctor to send both the nipple and vaginal discharge for a culture and sensitivity - so that it could be known if there is any bacterial infection associated or not.
Also discuss with your doctor about getting a ductography done to know the cause of the nipple discharge.
Has a mamogram been done? What is your sister's age?
This discharge is due to increased levels of hormones in the body or due to hormonal fluctuations - the nipple discharge is due to excessive prolactin; but whether a hormonal 'imbalance' is the cause can only be said after some blood tests.
Discuss the above in detail with your sister's doctor and see what he has to say. if you are still not convinced, ask him to refer you to a specialist.
Do let us know how your sister is doing.
Hope this helps.
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