Does this sound like a hacking, croup type of cough ? Any vomiting or excessive drooling? How old is she?
A dry, hacking cough that sounds like something might be stuck in the dog's throat is one of the symptoms of Kennel Cough. Bordetella Bronchiseptica has an incubation period of 2 to 14 days. It's often caught while dogs are boarded in kennels (hence the name) or even in dog obedience classes, dog parks, vet waiting rooms, etc.. It's more commonly passed along in poorly ventilated areas, thus the name 'kennel cough'. It's a bacteria which in normal situations isn't especially difficult to treat. There is usually a secondary infection (or more) that needs to be addressed in order to eliminate the problem, so a vet check is warranted.
In dogs with immune system or other problems, this could be a more serious condition and indicate urgent treatment to insure a better chance of survival.
Other causes for dog coughing are environmental, like cigarette smoke exposure, dust, temperature extremes (too hot, too cold) and even stress. It could be tracheal disease or just allergies.
Heartworm may cause coughing, shortness of breath and other signs of distress.
For more dog-cough information: http://www.canismajor.com/dog/cough.html
Also, there are 9 types of vaccines available against Bordetellosis, usually products with whole cell bacterin, extracted cellular antigens or avirulent live culture. Some are intranasal (rather than injectable). An interesting note is that among veterinarians, there is a differing opinion as to the necessity of these vaccinations, as well as how effective they actually are and whether or not the protection lasts.
Columbia Animal Hospital provides more http://www.cah.com/dr_library/kennekcough.html
Keep her calm and limit her activities - which may cause these spasms of coughing/hacking. As long as she's been drinking, just let her rest and make an appointment to be seen by her vet tomorrow.
If you notice breathing difficulty, lack of response, inability to get up, loss of balance, pacing and apparent refusal to lay down, crying in pain, vomiting with tinges of blood or diarrhea (especially with any blood), or fever - an emergency visit must be made.
To take her temp, using a digital thermometer, apply a dab of KY jelly or vasoline (even cooking oil or mineral oil) to the tip and insert it about 1" into the rectum.
Normal is between 100-102.5; if a temp of 104 or above is noted, this too is an emergency situation.
Just be sure to see the vet tomorrow ok?
Did you take the temp? Has this been going on just today? Where has she been walked? Any exposure to possible toxins like plants or chemicals (neighborhood, garage?)
Please make a call to your vet right now and use the emergency number or hotline if necessary.
Explain that this has been happening for three days and that it's "unproductive retching".
I would genuinely prefer this were kennel cough, but that you indicate it's more a vomiting (without vomit) action than a hacking, dry cough, you may be facing a serious intestinal/gut condition.
At just 10 years old, she's not that old. Please put that call in ok - and check back with me to let me know how it goes, what happens.
My prayers are with you and your companion. God bless,