Stumbling(Verb)
According to the dictionary Marriam-Webster the word stumblimg mean”To fall into sin or waywardness.”
Based on the last lecture, ”Sweat” by Zora Neale Hurston we read, ” she nearly fell upon the box in her stumbling.”
After I understand the word stumbling which mean fall down because of something, I understand more the quote above, that’s mean  she was get fall down by the nearly box.