Thanks so much for the answers to my questions.
Gum color is normal which is good as the fact that she may be a little lethargic, but not a lot.
When it comes to gastrointestinal issues, there could be any number of different reasons why she's ill ranging from dietary indiscretion (she ate something she shouldn't) or viral/bacterial infections to systemic diseases or inflammatory bowel disease.
But regardless of the underlying cause, the following would be my suggestions for her now unless she significantly worsens (in which case, I'd suggest you have her seen at an ER hospital, if possible).
1. Withhold water for at least 8-12 hours; she's not likely to become dehydrated in such a short period of time; just give everything a chance to settle down. If she hasn't vomited, then offer small amounts of water or pedialyte every several hours, but only a small amount at one time.
2. Withhold food for 12-24 hours and then if she hasn't vomited, offer a bland diet of 1 part boiled chicken (or hamburg or low fat cottage cheese) to 4 parts 20-minute white rice. Feed only a small amount at one time, 3-4 times through the day. I would not feed any regular dog food.
3. You can give Pepcid AC (Famotidine) which might help with the nausea. This is available at most human pharmacies. The dose would be 0.25 mg/lb twice a day. For example, the dose for a 20 lb dog would be 1/2 of a 10 mg tablet.
Other options include Prilosec at a dosage of 1/2 mg/lb once a day. For example, a 20 lb dog could be given 5mg once a day.
Zantac can be given at a dose of approximately 1 mg/lb which would be 1/4th of a 75 mg for a 20 lb dog twice a day.
Even Dramamine at a dose of 25-50 mg once to three times/day may be useful.
Meclizine HCl (Antivert is a brand name) is one such drug that could be used. It's an anti-histamine that can be used for motion sickness but it has anti-vomiting properties, too. The dose would be 2 mg/lb once a day. For example, if your girl weighs 20 lbs, her dose would be 1.5 tablets of a 25 mg tablet once a day.
Sedation might be seen as is common with some antihistamine drugs, though.
Once the vomiting is controlled (if it is) but if the diarrhea continues, then this could be addressed by using regular strength Pepto Bismol at a dose of 1/2 ml/lb 2 times a day. For example, if he weighs 20 lbs, then you would give him 2.0 teaspoons at each dose (5mls=1 tsp). It may change the stool color to a gray-black or greenish color though so this shouldn't concern you if it happens.
Pepto bismol should not be given to vomiting dogs since it contains salicylates (the active ingredient in Aspirin) which can irritate the stomach.
Consider probiotics such as Forti-flora. These may be available at local pet/grain stores. And continue the bland diet.
But if Belle becomes lethargic or continues to vomit, then I would suggest that you have her seen. Many dogs will respond to symptomatic treatment for gastrointestinal issues; if she doesn't get better, this doesn't necessarily mean that she has something bad but rather she might need stronger anti-vomiting drugs and anti-diarrheal drugs.
I hope this helps and that she feels better soon. Deb