
She does need a vet to check her over - do you know she doesn't have a retained puppy, for eg. Don't milk her - that only encourages lactation. The vet lshould be able to give her something to help scatter the milk. But that's just physically. Emotionally she needs to be taken out for some gentle exercise in the fresh air, to get her mind off what her entire system is telling her she should be doing at the moment.
Do you know why this happened?
Cut back on food, but as said not on water. Have you checked her temperature for fever?