In literal terms, you can't shake her off; both of them possess the Crane Cry Nine Heavens, with Qinggong enhancements. The opponent's realm Qi Power is even higher, so unless Chen Xuantian tears through, covered in blood, there really isn't a proper escape route. He can only helplessly follow her to fly towards Qingcheng Mountain.
However, after a few moves earlier, he had noticed it. There wasn't quite a need for him to flee hastily; he could very well fight.
Tang Xian'er's own abilities are actually not particularly strong, whether measured by Nascent Soul or Martial God standards, she'd only be considered average. Against the Outer Pill of the Immortal Palace, she might fare well enough, but regarded from the Cloud Platform, she's only second-rate at best, nothing more.
