First, talk to your previous boss - "那個男的" (dislike how you are calling him which shows no repect), confirm that she - "那個女的" is your future boss. YOu can check at HR as well.
Second, once confirmed that she is your future boss, try to get alone with her (don't mention the vacation again at this moment), report all work you are doing, and Pai-ma-pi, and discuss with her some future work. Whatever she ask you to do, you have to do it immediately and show your willingness to work under her leadership..... try to win her trust.
third, are you talking about the vacation this year? there are only 3 weeks to go, I don't think anyone will reject your pre-arranged vacation, unless the company is under fire and need you to fight it out.
Fourth, there is way that we don't want you to use - talking with her boss directly. If you have to take the vacation, and nothing can change you, and you don't care about her attitute to you in the future, and you can find a job easily, and you are a strong person can work under pressure with a criticising boss, then just go ahead and fight it out. I think you are on the right side, and she is on the wrong side. You can get your vacation.
Fifth, if she insist that you have to cancel your vacation, you might have to and then you can ask the company for reinbursment of the cancelling fee of your tickets. This is actually a good counter-attack to her plan. I don't think compnay typically pays this kind of expense, that leave you the opportunity to take the vacation.
Remeber, she is your future boss, and keep a good relationship is more importhant.
