I am sorry to hear that Brandy is losing protein.
It is important to know where it is being lost and what organs are affected in order to help her.
There are several reasons for low blood protein levels. Treatment will be based upon her disease process.
I would be concerned that your girl is suffering from a chronic disease process called protein losing enteropathy/nephropathy. That means both her kidneys and her intestines are diseased such that she cannot properly digest and absorb foods and is losing blood proteins through her diseased intestines and kidneys. This allows fluids to leak out of circulation and causes a swollen, fluid filled abdomen. This disease is one most commonly seen in younger female Soft Coated Wheaten Terriers and their mixes and Yorkies, but it can be seen in any breed.
Tests which can help diagnose the conditions are measuring blood albumin and globulin levels (both are likely to be low), measuring levels of fecal alpha1-protease inhibitor (API) concentration (should be high), and comparing the levels of protein loss compared to creatinine loss in urine (should be higher than usual).
A definitive diagnosis is achieved via biopsies.
If this is the case it may help to feed a hypoallergenic hydrolyzed diet and give drugs to decrease protein loss via the kidneys and hypertension (Enalapril or Benazepril). Steroids may be indicated as well.
Another possible cause for low blood proteins is a portosystemic shunt, which is an abnormality in the blood vasculature that feeds the liver. The liver is responsible for making blood proteins and if function is poor and proteins aren't produced then we can see low blood protein levels, free fluid in the abdomen, and diarrhea. This is usually a congenital condition, meaning that the dog is born with it, but symptoms may take time to develop in less severely affected dogs.
If her liver appears small and her liver function is abnormal (abnormal bile acids test) then a portosystemic shunt (congenital abnormal liver vessel anatomy) would be a reasonable tentative diagnosis. Then she would need further testing to determine the type of shunt (single or multiple vessels as well the location of the shunt - inside the liver or outside). Treatment will be determined by the type of shunt. If the shunt is a single one out side of the liver and can be successfully occluded without raising blood pressure within the liver then surgery is the way to go.
If the shunt is involving multiple small vessels within the liver or if when the shunt is occluded blood pressure within the liver rises then medical/diet therapy is the way to go.
I'll give you a link which discusses the different shunts as well as surgery and medical treatment which I hope will be helpful for you:
And here's another that is a little more about medical treatment:
It sounds to me like you do not have a firm diagnosis for Brandy and further testing needs to be done to determine the primary cause of her condition.
Please let me know if you have any further questions.