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An intact (un-spayed) female dog who is experiencing excessive thirst and vaginal discharge, soon after finishing a heat cycle, is highly suspected of having a serious infection of the uterus, known as Pyometra. This is a life threatening condition, and I would strongly recommend seeing a veterinarian as soon as possible.
The fact that there's visible discharge, suggests that her cervix is "open", which is less serious than if "closed", but either way, this is a serious illness that requires evaluation sooner rather than later, and I would strongly advise not waiting to seek veterinary attention.