Hi, Thanks for writing to HCM. Lasix contains furosemide. It is a diuretic drug, which will eliminate excess collection of water from the soft tissues through passing of urine. Since it causes loss of potassium, she must be experiencing leg pain as the side effect of the drug. Instead, to decrease her swelling in the legs, she can be administered potassium-sparing diuretic like Spironolactone. She should tolerate this drug better than lasix. Kindly consult Physician in this regard for the change in drug and proper dosage depending on her clinical condition. Hope the information provided is clear. All the best.