Idiopathic Edema: This condition is characterized by swelling in the legs and hands without an obvious cause, often seen in young women. The normal laboratory results, including normal TSH, creatinine, ECG, echo, and absence of anemia, along with the presence of 1+ protein in urine without RBCs, support this diagnosis. The normal UPC ratio and USG findings further point towards a non-renal, non-cardiac cause.

Nephrotic Syndrome: Although the UPC ratio is normal, and there's only 1+ proteinuria, early or mild cases could present similarly. The absence of significant proteinuria and hematuria makes this less likely, but it remains a consideration due to the protein in the urine.
Lymphedema: This could be primary (inherited) or secondary (due to another condition). The bilateral involvement and absence of other symptoms or findings suggestive of secondary causes make primary lymphedema a possibility.
Hormonal Influences: Fluctuations in hormones, especially during puberty, could lead to fluid retention and swelling. The normal cortisol level does not entirely rule out hormonal influences, as other hormones could be involved.

Renal Diseases (e.g., Minimal Change Disease): Although the urine analysis shows only 1+ protein and no RBCs, and the UPC ratio is normal, certain renal diseases can present with minimal or intermittent abnormalities in urine tests. Missing a renal disease could lead to significant morbidity.
Cardiac Conditions (e.g., Early Cardiomyopathy): Despite a normal ECG and echo, very early or mild cardiac conditions might not be detected. These conditions can lead to edema and are critical to diagnose early.
Thyroid Disorders: Although the TSH is normal, thyroid disorders can sometimes present with atypical symptoms, and edema can be associated with both hypothyroidism and hyperthyroidism in rare cases.

Fabry Disease: A genetic disorder that can lead to edema among other symptoms, due to the accumulation of a particular type of fat in the body's cells.
Klippel-Trenaunay Syndrome: A rare condition characterized by port-wine stains, varicose veins, and swelling, typically affecting one limb but can be bilateral.
Protein-Losing Enteropathy: A condition where the gut loses protein, leading to low levels in the blood and potentially edema. This would be unusual in the absence of gastrointestinal symptoms but could be considered if other diagnoses are ruled out.