Training her protege.

"Tch!" Grandma Zhang pursed her lips. "Calling it harming is too much. A mutual union basing on arranged marriage between two families is not harming anyone. I am sure the woman will also agree with me." 

"Then consider it harming your son mother." he reiterated. 

Grandma Zhang looked at her son for a moment, and noted the willfulness in his eyes. In there, she could see traces of her old son, the one who had a backbone and could stand his ground. It convinced her that all she would be saying after this would not be taken in. He would ignore her wishes and do as he pleased, just like his sons. 

"Alright, i am going to surrender for now but i don't want you to imagine that i am a villain in this scenario. I want you to get married because i am worried that you will be lonely in future. Your father and i are already this old and we are not getting any younger.