I'm thinking mostly like a cotton/jersey maxi dress for this occasion but any other could apply to.

My girlfriend's favorite maxi hits like right at/below her ankles but whenever she wears it in the shower it stretches to the point where it's pooling on the ground a good bit.

My question is- if you wanted to make a dress longer, would you have to wet all of it, or could you just wet the bottom couple of inches?