Hi, thanks for using healthcare magic Because the coughing can be related to fluid accumulation in the lungs secondary to the heart disease, it would be best that she is assessed by her doctor before any other medication is used. The doctor will listen to her lungs to see if fluid is present, if it is then she would need an increased dose of the lasix. There are other causes for cough such as asthma, post nasal drip , a viral infection, pneumonia or gastroesophageal reflux. These would be considered if fluid accumulation is ruled out. I hope this helps