I am afraid she may be bleeding internally in her stomach rather than from her mouth. If you can see a spot in her mouth that is bleeding try applying ice to it to slow the bleeding and promote clotting.
If she is vomiting blood she may get some help by using a human antacid. Milk of Magnesia, one teaspoonful per five pounds body weight may help orfrom this site
Tagamet (Cimetidine) Tagamet is administered at a dose of 18 mg per 10 lbs., 4 times a day. This means that a 10 lb. dog should receive 0.3 mL (60 mg/mL) of the oral solution, or a 0.12 mL (150 mg/mL) injection. A 50 lb. dog should receive 1/2 of a 200 mg tablet.
Zantac (Ranitidine) Indications for Use: This product, formulated to help prevent ulcers, should be used in animals that are experiencing stress or have digestive tract ulceration.
A dose of 9 mg per 10 lbs., administered three times a day, is recommended. This means that a 10 lb. dog should receive 0.60 mL (15 mg/mL) of the oral solution, or 0.36 mL (25 mg/mL), SQ or IV of the injectable form. A 50 lb. dog should receive about 1/3 of a 150 mg tablet.
If you can get anyone to help you give her subcutaneous fluids or an IV like the vet did (maybe a medical doctor or a emergency paramedic person can help) that might help her.
The rapid breathing is probably from pain and stress. If she is bleeding from an open ulcer or cancer or from having ingested a poison she will probably get very tired as she loses blood and fade away on you.
If she is thirsty and you can get her to drink pedialyte (plain) or Gatoraide or someother electrolyte solution that may also help.
I hope she makes it for you.