You may want to consider having her seen by a cardiologist. There are many medications available now that significantly help prolong life and quality of life for these cardiac dogs. In order to find the correct balance for her, the cause of the heart failure needs to be addressed as well as the failure. Heart failure is a general term to describe the stage of disease- it means that the body is producing fluid in or around the lungs or in the abdomen. It is not a diagnosis. There is a list of cardiologists in the US on http://www.cavalierhealth.org/Cardiologists.htm
Also know that there are problems that can lead to or result from heart disease including collapsing trachea which sounds like a honking cough due to restriction of air flow. Collapsing trachea is common in smaller breeds such as Maltese. It can easily be tested through palpation of the trachea, x-rays, or tracheobronchoscopy (endoscopy for the trachea.) This can cause coughing alone and can also put a strain on t he heart and lungs. Dogs can also can have scaring of the lungs which can both add to the heart problem and coughing.
In either case, the use of the supplement slippery elm may be beneficial- this is not going to correct the issue but may decrease coughing. It can be purchased at a health food store or anywhere else they sell supplements. Slippery elm capsules can be opened, mixed with a tablespoon of water and ingested when it reaches a syrup consistency.
However, your girl can be helped with proper medication. There are so many heart medications available but they each do something different. Without having proper diagnosis, you or your vet can not be sure the right medication is being used. If she were mine I would find a Cardiologist for her to see or have her current vet consult with one. It is very common to do such things with cases like this. It is most important that your dog gets started on the right medication ASAP to give her the longest and most quality filled life possible.