According to the reading of the lines presented, we can infer that the Abuelita was locked for the second time in the warehouse by its own will. That's because she wanted to test the power of the whistle, watching not only if her granddaughter could hear how she was able to whistle back. This strategy of being trapped by Abuelita left her with a feeling of being a very intelligent and shrewd lady.
We can confirm this when the granddaughter says "I could see that she was smiling, and I think I even heard her chuckling."
