She is lethargic and laying here shaking she just threw up all the water and food she ate. A Three year old female

I’m Dr. Roe and I’m happy to help you. While this forum is strictly for advice as we cannot make diagnoses, dispense medications, nor establish doctor-patient relationship, I can offer guidance and support.

Sometimes a heat cycle can make them feel yucky.  I would withhold all food x 8-12 hours. You can offer water, dilute broth, or pedialyte in small quantities (1 cup every 2-3 hours) to prevent her from guzzling a large volume which could restart the vomiting cycle. Also start over-the-counter pepcid dosed at 0.25mg per pound of body weight by mouth and repeat that dosing every 12 hours x 4 days. This is an antacid that can be found at any human pharmacy and will help to settle the stomach. Once she has not had any more vomiting, then you can start offering a bland diet of boiled chicken and white rice 1 cup every 3-4 hours increasing the portions and decreasing the meal frequency over the next few days. Should these issues persist, then she should be seen by your veterinarian.