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Sorry to hear about Jessica,
I would advise that you contact an emergency vet's tonight as this sounds very urgent. She may be very dehydrated from vomiting, or may be suffering from other abnormalities such as electrolyte disturbances or bloating of the stomach etc. There are several different things which can cause lethargy and vomiting but her not being able to stand is very urgent and it is important she is seen by an emergency vet tonight to prevent any deterioration.