I would have tolerated Rose interrupting Finn’s sacrifice if she had said something like, “I lost my sister, and I couldn’t bear to lose you as well.”
Instead she gives this horrible lecture about how she saved him—he didn’t need saving, he was making a selfless sacrifice for his friends. Instead of running away, he was finally committing to the Resistance and doing something incredibly selfless to help the people and cause that he had come to care about.
Rose comes along out of nowhere and interrupts that, and then has the nerve to lecture him about how you are supposed to fight for the ones you love. That’s exactly what he was doing, stu pid Rose!