She is holding enormous amounts of water in her legs, well all over, so she's not wrong when she says she has water weight. If it goes untreated, then her legs will puff up, leak fluid, at a high risk of infection, and the worse case the skin will rot.
For others curious about AL's Lymphedema and what it is:
What is Lymphedema?
"Lymphedema swelling that occurs when fluid drained by the lymph vessels does not flow out of the arm, hand, chest and upper back, groin, legs"
What makes Lymphedema worse?
"Sodium Sodium (salt) can worsen lymphedema Refraining from adding salt to food while cooking or at the table. Avoid high-sodium foods like processed foods, deli meats, canned vegetables and soups, condiments, frozen or convenience entrees, savory snacks, certain cheeses, pre-marinated meats and fast food. "
What stage is AL in?
Stage 2:
"Swelling takes on a spongy consistency and “pitting” is less present. Does NOT respond to elevation. Fibrosis, or scar tissue Gradual thickening of the tissues on the limb as it increases in size."
"When lymphedema remains untreated, it will progress. "
source:
https://slideplayer.com/slide/3451276/
If AL doesn't get treated, it will look like this [WARNING: GRAPHIC]: