That whole thing with Rose and Finn was the biggest WTF in the entire movie for me. For one, Rose was the younger sister of someone we'd seen die valiantly, and I thought she was supposed to be like 12 years old, but okay I figured you're never too young to join the resistance. Then they went on that whole mission to find the hacker, didn't find him but did manage to find a guy who claimed to be a hacker, but then he betrayed them and the mission failed. Nice waste of half an hour there.
Then Finn is ready to sacrifice himself to take out the nuclear battering ram thing, and Rose takes him out. Why!? After wasting the entire movie, I figured Finn was gonna at least go out with a heroic exit, but no. Somewhere in there, she kissed him, and I finally realized that she's not supposed to be 12. 15 maybe? But that whole thing made no fucking sense.