The man in black looked and realised that the person who had given her the powerful, precise kick was a tall man who was obviously anything but frail. If she continued to put up a fight against the man, not only would she fail to kill Xu Weilai, she might even be subdued and it wouldn't be worthwhile.
However...
The man in black narrowed her eyes and decisively gave up on the idea of getting her knife back. Instead, she suddenly charged towards Xu Weilai, who had let down her guard, and pushed her towards the edge of the cliff violently.
The force made Xu Weilai fall forwards.
The man horrified and, without any hesitation, pounced towards Xu Weilai as best as he could. Grabbing hold of her wrist tightly, he managed to pull her back up before she fell off the cliff.
The man in black then used the opportunity to retrieve her knife and escape.