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Hello, this is Dr. Jess. I am very sorry to hear about your dog Heidi. Unfortunately if she has been vomiting for over 3 days, it is really past the time the time that at home care is usually used to treat the condition. If she cannot even keep water down, and it has been going on since Monday, she is going to need an exam, possibly an x-ray or bloodwork, and injectable medication since she cannot keep anything down.
The things we sometimes try at home when vomiting has just started include a period of fasting (no water and food) and slowly reintroducing liquids and then bland food such as rice and boiled chicken breast, and sometimes giving a dog pepcid. But if it has been going on for 3 days and she is vomiting even just water, this isn't going to work for her. She is likely getting dehydrated and is going to need some fluid therapy (via an IV or under her skin) to get her hydration back.