I am sorry to hear that your little one Lattoo isn't feeling well today, vomiting foam twice, dark liquid twice, lethargic and just not herself.
Vomiting dark liquid can be a mix of stomach and esophageal juices and pigments form food she has eaten.
If the color was dark yellow that can indicate bile. Yellow in the vomit can mean that the small intestine is refluxing bile into the stomach so that when she vomits you see the yellow color. That isn't normal as bile doesn't belong in the stomach, and it does mean that there is some reverse motility, but it isn't specific for any particular disease process.
Vomiting foam simply is a mix of air and stomach/esophageal mucous made when she retches, it is not indicative of any disease process but tells us she is quite nauseous.
Is she running a fever (rectal temperature greater then 103F)?
Does she have a tense, painful abdomen with gentle pressure on her belly with your hands?
Vomiting and nausea can be due to stress, a change in diet, parasites, a viral or bacterial infection, eating something she should not (like a piece of a toy or string), inflammatory bowel disease or even a food allergy. But it can also be related to metabolic organ disease (such kidney or liver disease) due to organ wastes irritating the gut or an obstruction in the gastrointestinal tract.
Ideally because she is continuing to vomit and is lethargic she should see a veterinarian.
If that isn't possible today then it may also be helpful to put her on an acid reducing medication as stomach acid, especially on an empty stomach, is very irritating and predisposes to continued vomiting.
You can give either:
1) Pepcid ac (famotidine) at a dose of ¼ of a 10mg tablet per 2 to 5 kilos of body weight every 12 hours
2) Prilosec (omeprazole) at a dose of ¼ of a 20mg tablet per 5 to 10 kilos of body weight every 24 hours
3) Ranitidine (Zantac) at a dose of 1/4 of a 75mg tablet per 18 kilos of body weight every 8-12 hours.
These acid reducers and may help her feel better. They are quite safe and can be used for several days if necessary.
With-hold food for a good 12-24 hours. This should help stop gut spasms and restore normal gut motility. Small amounts of water or ice cubes starting in a couple hours after the acid reducer and given frequently are fine as she needs fluids after all that she has lost with not eating. You can give her pedialyte or low salt broth to replace electrolytes too, but Gatorade is much too high in sugar which can make her stomach more irritated.
If she stops vomiting after her food fast start a bland diet of 1/3 boiled, lean hamburger (or boiled, white skinless chicken), all fats drained off the meat, mixed with 2/3 boiled, plain white rice. Feed several small meals a day. I recommend adding probiotics like Fortiflora, Proviable or Benebac to her meals daily to re-establish normal gut bacteria levels too.
Once she feels better (eating well and no vomiting for 48 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 continues to vomit even with the acid reducers, runs a fever (more than 103F rectally), has a tense painful belly or if she refuses to eat she should see a veterinarian for an examination, and some diagnostic testing. I would start with a complete blood count and biochemistry profile, a specific test for pancreatitis called canine specific pancreatic lipase, as well as fecal checks for parasites.
Please let me know if you have other details or a particular question based upon my response.