Well, she was thoughtful, and it is felt that she thought deeper about things and thus figured it out. She was the oldest of the girls,if not the most practical, and was the most intellectual. She had seen the most, and with her deeper nature was able to perhaps see, though we don't know for sure, nor how much. But I think she sort of knew, and accounts hint at this. I think she kept her spirit, but it would be hard to in these circumstances, with realization. Looking at it from hindsight, we have to remember that none of the Romanovs knew they would die that night, but Olga could have sensed some sort of doom.