I am not sure both letters would send if only one is required. Here is a video that shows how it works, I don’t know if the school has any leeway on how to set this up, but I doubt it…and the GC does NOT control this action, the student does.
Here’s what the screen looks like, where the select their teacher(s), and then choose which colleges each LoR should go to.
Here are Naviance’s directions: https://sites.google.com/berenacademy.org/naviancehelp/letters-of-recommendation?pli=1