Ji Mao'er was a stupid girl and it was easy for Jiang Yao to control her. And she made use of the stupid girl to get rid of all the contestants. All she had to do was provoke the stupid girl and all the roadblocks would be cleared for her.
However, as time passed, her own 'friends' became her stumbling blocks. The reason why Jiang Yao befriended Xiao Xinyi and An Xiulan was that they were weak contestants and she never overestimated. She became anxious when both of them entered the top five.
Jiang Yao arranged the water armies to soil the image of An Xiulan because it was the lost harmless way to hurt that cute girl. She didn't have the heart to hurt An Xiulan because she genuinely like her but she wanted to win. She wanted to win at any cost to enter Miss China.
She placed the nail in the grass to harm Ji Mao'er. At most, the nail will pierce through Ji Mao'er feet and she wouldn't be able to walk.
