The moment Lin Shuang received the call from Qin Fang, she knew who the caller really was. Thus, she didn't hesitate to reject the call.
She had once considered explaining things to He Yidu, but she didn't know what she should say. If she were to say that she blocked him because she realized that she was a bit fond of him and didn't want her feelings to affect herself, it would be no different from a confession, and she would be giving him hope when she had no intention of doing so. Hence, she had no qualms about blocking him. She wanted to end things as fast and clean as possible.