Kendra is trying to decide whether to go to Abby's house to watch a movie or to go to Samuel's house to play board games. They live about the same distance away, and there is no cost for either event. If she chooses to go to Abby's house, what is the opportunity cost?

There is no opportunity cost because there is not cost associated with either option. Economics do not apply to this kind of decision.
The net value to Kendra of going to Samuel's house to play games.
The net value to Kendra of going to Abby's house to watch a movie.
The difference in value to Kendra of the two options.

Without knowing Kendra's preferences, it is impossible to determine the exact net value of each option to her. The net value could depend on factors such as her enjoyment of the movie or board games, her relationship with Abby and Samuel, and other personal preferences. It is ultimately up to Kendra to determine which option she believes will bring her the most value.