Bai Ruozhu was sure that these people were not targeting Jiang Yichun, since their level of proficiency posed no harm to him, failing to perform effective assassination. She had seen attempts on Jiang Yichun's life before, and those were far more lethal than a mere handful of dark arrows.
However, if Jiang Yichun weren't present, these small dark arrows would've likely hit the horse carriage. Even if they didn't injure anyone inside, they would've horrified the women in the carriage.
Moreover, all arrows were aimed at her carriage, clearly indicating the target. Her sister-in-law and Guizhi rarely made enemies, not enough for someone to put so much effort to assassinate them. As for Yu Hongxiu and Mr. Xie, who previously resided in Anyuan Town, if anybody sought to kill Yu Hongxiu, they would've tried long ago.
Hence, the target was undoubtedly her.