It may be an innocent sentence saying that she drinks a lot of water, but the chances are that this implies she's alcoholic.
Must be gallons of alcohol for a fellow pole to even admit that it's a lot.
Yes, in the states we would often say, she's a lush or a sot, boozer, rummy. That's what makes the language so difficult for outsiders to grasp. It certainly gets colorful at times. If you're a nmtive.
Not here. „Dość!” as standalone word means „Enough!”. In order to insert dość here we would have to write: „Ona dość dużo pije" -> She drinks quite a lot.