According to Henry Alonso Myers:
The Una piece is absolutely a cliffhanger. Part of that was because we felt like there was a big chunk of her story that we had yet to tell. We really wanted to dig into it and we had an idea about how to do a real straight-down-the-middle classic Trek episode in order to tell the next piece of her story, which we get into next season.
I admit at the time, when Akiva and I put that bit in there about Una in the Season 1 finale, we didn't really know how we get out of it. Sometimes at the end of the season, you want to pull as many threads as possible because you want to leave yourself somewhere to go. But since we're almost wrapped for Season 2, I do happen to know where we went and I'm really glad we did because I'm unbelievably proud of the Una arc that came out of it, and I can't wait for people to see it.