When Liu Hua had said that she knew what tricks Li Xue would fall for, she wasn't joking. For just this one reason and just for this one day, she was happy that she shared the blood with the girl. Maybe that one connection has enabled her to have one trick against her up her sleeve.
Liu Hua has long guessed that even if Li Xue comes to the engagement of Sying, she would be coming with full guards on, which would also include her not touching any food or drinks offered to her. So, to trick her for the good, she has planned everything in accordance.
She has not drugged any glass drinks that were being offered to the guests, rather she has asked someone to drug the sealed bottle of mineral water that Su Fai has got for Li Xue earlier. Since it was delivered by her friend, Liu Hua knew that girl would accept it without any special thought, the same as she did earlier. She didn't prove her thoughts to be wrong.