Yu Dong always has a plan
Yu Tong had been staying with Yu Dong ever since the incident took place on the day the village was flooded. Strictly speaking, she had never even visited the Old Yu family house, thus it was quite a surprise for Yu Dong to hear that Yu Tong had been engaged.
Either Yu Tong hid it from her or Second Madam Yu was the one who decided everything without telling Yu Tong. As Yu Dong was very much aware of what kind of person Yu Tong was and how much she loved Lin Hanjing, there was no way she would agree to get engaged to someone else.
So most likely, it was Second Madam Yu who decided everything on her own.
"This is going to be very problematic," Yu Dong remarked with a frown. If the engagement was already publicized to the point that the entire village was aware of it then it could only mean one thing —— Yu Tong would not be able to back out of the engagement.