I think that we should stick to simple terms here....Swollen legs and Lyphoedema are two different things with mainly if not always ,different causes.
Your mother has swollen leaking legs because she has had failure do almost certainly to poor circulation to the heart.
Water tablets is the treatment of choice as well as attention to other underlying conditions such as diabetes or high blood pressure.
There are ,as Buenchico stated, other causes,but in your mother's case, extremely unlikely.
If she can keep her legs raised, that might help and although you haven't mentioned which Water tablet she is taking and what dose, then I cannot help further.
She could return to hospital to monitor and initiate a forced diureses( make her pass more urine),but I think that would be unacceptable and perhaps cruel to all sides.
Her heart is failing and all you can do or indeed anyone can do, is to make her comfortable........not as easy as it sounds.