Okay, lasix is not a drug we arbitrarily start without a definitive diagnosis of congestive heart failure and fluid accumulation in the lungs. When it is prematurely started, and there is any other lung disease or infection that could be contributing to a harsh cough, it will dehydrate the pet, possibly thicken mucoid secretions in the lungs, and make them worse.
The same thing applies to potassium supplementation. We generally do not give it unless we have a blood test that shows potassium is lower. This is a very common mistake made at home. We frequently diagnosis hyperkalemic pets that can een result in heart arrhythmias when they are supplemented potassium incorrectly or excessively.
If I were you, I would not suggest giving either until your vet can do an exam and some basic testing to confirm what is going on. That is particularly true with these two medications.
Lastly, the swollen abdomen. Let's "assume" it were fluid. Lasix is poor at helping to pull fluid from the abdomen. It is far more successful when there is fluid accumulation in the chest due to congestive heart failure. Plus, there are many other conditions that can cause the swollen belly appearance including organ enlargement and Cushing's disease.
Definitely, well worth consulting your pirmary vet first before giving anything.
Hope that new information helps