Everything happens slowly. Almost every process in the world is gradual, nothing happens with a snap of fingers, almost immediately. Everything happens with its own time frame.
Just like the first bottle of scotch, it was finished in a month. The second bottle was in two weeks and she realized that the third bottle she had hidden in her room was the only bottle left.
If they carry down, then there was no way she would have a source to help herself. The thing was, Darla had taken upon herself to fix the reins of the house, and she had done it immediately after Joyce gave her a brief run down. It was like she knew exactly what to do.
That also included getting a lock on cabinet doors and pantry including the alcohol cabinet. It felt like Darla was intelligent enough to make it seem like she was looking at every cabinet in the house, not just the liquor one.