If sending an email won't work despite the offers she had presented then she doesn't have any choice but to visit her personally. Furthermore, the sooner this will be done, the better since she can't do without a competitive assistant with her full blown schedule.
People might think that being an assistant only means that you have to follow your boss everywhere but what they don't know is that being an assistant is more than that.
Even the simple act of arranging the schedule for a boss as busy as her is already an arduous task. On top of that, her assistant should also be well versed in English as it is an international language and most of all the assistant should be able to adapt quickly to the changes around her.
Well, she would just mind this matter in a while for now she should just focus on talking with Wang Xinyi.