Can you recommend a time-travel novel where the heroine was a killer or agent?

It seemed that the female protagonist was sent by her father to the male protagonist to monitor him. It was unclear whether the male protagonist was the emperor or the prince. At first, the male protagonist was very disgusted with her, but after the female protagonist transmigrated, she changed. Because the body structure of the transmigrated body was too bad, she started to exercise, jogging in the morning and doing yoga. Later, the male protagonist gradually fell in love with her, but the female protagonist never accepted him. He remembered that there was a plot in which she made a pair of jeans and skates, and then she was frozen on the frozen lake. There seemed to be an old man inside, who seemed to be the master of the male protagonist or someone else. He was very close to the female protagonist, just like the old playboy. When he saw the female protagonist skating, he also made skates to go skating. The female protagonist also pulled a lot of strings in a room, just like imitating infrared rays. He couldn't touch the old playboy and let him challenge her. The female protagonist seemed to know a lot about military affairs and would give all kinds of suggestions. This was all she remembered for a long time.