Xu Weilai was injured and her movements weren't agile enough. Furthermore, the man in black was bent on killing her and possessed a weapon. She would not gain anything if she were to fight her assailant head-on and thus, the best solution was to escape.
Xu Weilai immediately began to make a run for it.
She does not know which way to go to head down the mountain but she had no time to think. She could only choose her path based on her instincts and tried her best to maintain a distance between herself and the man in black.
Fortunately, as she had been working out with Simon during this period of time, she had almost fully regained her physical fitness. Pain from her wound made her break out in cold sweat, but she still persevered and continued to run.