16-year-old Helena Muffly wrote exactly 100 years ago today:
Sunday, October 29, 1911: Went to Sunday School this morning. Tweet came along with Ruth from church. So you see she was here all afternoon. Ruth and I went up to Oakes’ this evening.
Her middle-aged granddaughter’s comments 100 years later:
Grandma’s monthly exams were scheduled to begin the next day. It seems odd that Grandma doesn’t mention studying for them in this diary entry. The previous Thursday she had mentioned that she was struggling in algebra and worried about upcoming exams. And on Friday, she’d written that she “must begin to get ready for upcoming examinations which come around again next Monday and Tuesday.”
Yet she never mentioned studying on Saturday or Sunday—and apparently spent most of Sunday with friends. The Oakes lived on a farm near the Muffly’s. Several of the Oakes children were close in age to Grandma and Ruth.And, earlier in the day another friend, Helen Wesner (who went by the nickname of Tweet), visited them.
A Hundred Years Ago 
Perhaps your grandmother needed a break from studying so she be refreshed and ready for her exam.