3 year old addicted to milk!

She only wants to drink milk! It getting ridiculous I’m not kidding when I say she can drink half a gallon a night!!! If we don’t give it to her she cry’s and wakes her baby brother up so we just give into her. She uses a cup and drinks it so fast then cry’s for more saying “she’s so thirsty” idk what else to do it’s getting annoying having to get up hours of the night just to fill her cup up & having to always buy milk. It’s 2% milk by the way. If I say no she throws the biggest fit. Please help! Yes I try to ignore get it don’t work she’ll cry louder and louder.