Friend, when we see quick onset of unwilling or the inability to get up in a dog this could be caused by many different medical conditions. In general we can classify this either a neuromuscular problem (a bulging disc, vestibular disease, thromboembolic, etc.) or secondary to a systemic disease like an abdominal tumor, heart disease, toxicity, etc. to name a few causes. The vomiting is secondary to what is causing her the inability to stand. The shaking could be a sign of pain or weakness.
On history alone it will be difficult to determine the exact underlying cause. Unfortunately we are very limited as to what you can do at home. I would strongly recommend having her checked by a veterinarian as soon as you can. It is important to rule out things like abdominal tumors, thromboembolic, etc. which can have a fatal outcome if not treated promptly. I realized this is your friend's dog, I would give him/her a call immediately to make them aware of the situation. In the meantime for the vomiting this is what you can do:
1- Do not give things like Pepto Bismol or imodium. Start her on Pepcid AC (famotidine) 0.1-0.2 mg per pound body weight every 12 hours. You can buy Pepcid AC over the counter in any pharmacy.
2- No food or water for 4-6 hours. Need to give her gastrointestinal tract time to rest.
3- After 4-6 hours offer a small amount of water. Wait half hour, if no vomiting, offer small amount of rice (50%) and boiled boneless chicken or ground beef (50%) 4-6 times a day.
4- Follow up with a veterinarian for a hands on examination as soon as you can.
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