I redownloaded the game with the latest version (wasn't aware there was an update as I could not find any community posts about it). DLC worked fine when I did that.
Viewing post in Love and Sex: Second Base - For A Fistful Of Waifu comments
While running game code:
File "game/dlc_fafow/setup.rpy", line 2, in <module>
TypeError: list indices must be integers or slices, not str"
If you have this exact error, it means that your dlc version is not up to date.
Remove the dlc file from the renpy save folder.
Launch the game.
Download the latest version of the dlc file, and put it back in the correct folder.
Launch the game again.