Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am very sorry to hear about your Daisy's vomiting food several hours after eating and her more subdued manner , but I am pleased to hear that she is drinking water and keeping that down.
Vomiting/retching can be from several causes. Common ones are a quick change in diet, too many treats, especially fatty or spicy treats, eatings things they should not such as things found in the yard, toy pieces or garbage, viral or bacterial or parasitic infections.
More serious causes include chronic pancreatitis, esophageal reflux, a dietary allergy or sensitivity, inflammatory bowel disease, internal organ failure (kidney or liver disease, diabetes), a full or partial gastrointestinal obstruction or even infiltrative cancers such as lymphoma.
Since she vomited food several hours after eating that points toward slower than usual stomach emptying and may indicate a partial obstruction. Please look at her toys or around the yard for something she may have eaten.
At this point we can try some things at home but he may need to see a veterinarian if she isn't coming along well or something changes with her.
To try and settle her stomach you can give either:
1) Pepcid-ac (famotidine) at a dose of one 10mg tablet per 20 to 40 pounds of body weight every 12 hours.
2) Prilosec (omeprazole) at a dose of one 10mg tablet per 20 to 40 pounds of body weightevery 24 hours.
These will reduce stomach acid and should help if this is related to simple nausea and gastrointestinal irritation from eating something she should not have. They can be given for several days if necessary. I understand that her veterinarian prescribed famotidine, but I wanted to make sure that you are giving an appropriate dose, and if so then perhaps Prilosec (omeprazole would be better for her).
Starting a couple hours after the acid reducers small amounts of water or clear broth mixed with a little meat baby food is worth trying.
You can give her pedialyte to replace electrolytes too.
If things are going well after she is given liquids then in a few hours restart a bland diet of 1/3 boiled, lean hamburger (sine she vomited chicken), all fats and juices drained off the meat, mixed with 2/3 boiled, plain white pasta or mashed white potatoes. Feed several small meals a day. Once she feels better (no vomiting for 48 to 72 hours) start mixing in her regular dog food very slowly. Less bland more regular with each day. It should take a week or so to convert her back.
If she is continuing to vomit it would be best that she see a veterinarian promptly as anything you give her orally will just come back up leading to dehydration. They can check blood tests (complete blood count, biochemistry profile and a canine specific pancreatic lipase) and a urinalysis to look for underlying organ disease and possibly an abdominal ultrasound to look for a foreign body or mass in her abdomen.
If she has a tense painful abdomen, becomes very lethargic, begins vomiting again or runs a fever greater than 103.5F then she really must be seen by a veterinarian as soon as possible.
Best of luck with your little one, please let me know should you have any further questions.