In order to prove her guess, Yu Wan found Xianglian and obtained the Gu that she was originally going to use on Yan Jiuchao.
According to Xianglian, she had already been poisoned. Yu Wan asked Little Gu to pull out the Gu in Xianglian's body. When the two Gu were combined, it was indeed a Love Gu, and it was the Amorous Gu, that was known to be difficult to part with.
If she had to ask how she recognized it, it was all thanks to Ah Wei. When she went to the Nether Capital, she had learned a lot of knowledge about Gu worms from Ah Wei. Among them, the one that left the deepest impression on her was this Amorous Gu.