I am sorry to hear that Daisy Mae isn't feeling herself, with a sudden decrease in appetite. I am pleased to hear that she is continuing to drink water.
How long has this been going on?
Any vomiting or diarrhea?
Possible causes of her symptoms include a quick change in diet, dietary sensitivities or allergies, or eating things that they should not like too many fatty table scraps or garbage, bones etc., or a systemic infection. Metabolic organ failures (kidney or liver disease), Addison's disease (hypoadrenocortisim), pancreatitis, inflammatory bowel disease, an abdominal mass putting pressure on her gastrointestinal tract making her feel full, or even infiltrative cancers are other possible causes.
Ideally if this has persisted for several days I would recommend an examination and checking basic blood tests on her including a complete blood count, biochemistry panel and a blood test for pancreatitis called can spec PL (canine specific pancreatic lipase) which is highly specific for pancreatitis. If her electrolyte levels seem unbalanced (high potassium and low sodium) then testing for Addison's disease with a test called an ACTH response test.
If those things are normal then the next step diagnostically would be an abdominal ultrasound and endoscopy to collect intestinal biopsies.
Has she been fed anything different or gotten into anything different that you know of?
In the meantime to help with gastrointestinal upset and reflux 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 20mg tablet per 40 to 80 pounds of body weight every 24 hours
These are acid reducers and should help her feel more comfortable. They are quite safe and can be used for a few days if needed. In some cases dogs remain on them long term if this is a repeated problem.
In a couple hours offer her low beef or chicken broth to drink but make sure it is in small amounts only. If she drinks too much too quickly that can lead to nausea and vomiting. To get some electrolytes in you can also offer her a 50:50 mix of pedialyte and water.
If she seems to feel better a couple hours later offer a bland diet mix of 1/3 boiled, minced, white, skinless chicken or boiled, lean hamburger and 2/3 boiled, plain, white rice or pasta mixed with some low salt chicken or beef broth to make it easy to lap up and swallow as well as increase her fluid intake. If she refuses that you can offer a little meat baby food. Probiotics such as Fortiflora, Proviable, or Benebac can help replace appropriate bacteria. You can add those to the bland diet mix.
If things go well and she does eat and doesn't vomit feed her the bland diet for 2 to 3 days then slowly start to mix back in her regular food, a little more at each meal. It should take about 5 to 7 days to slowly convert her back to her regular diet.
If she continues to refuse to eat, begins to vomit, runs a fever (more than 103F rectally), has a tense painful belly then she is not a candidate for home therapy and must see a veterinarian for an examination, diagnostics, injectable anti-nausea drugs intravenous fluids and supportive care.
Please let me know if you have any further questions.