A1: Just give her one month notice before the end of the 2-year contract or you also can pay one month salary in lieu of one month notice. That's mean you ask your domestic helper leave your home at the end of 2-yr contract without notice.
Under HK labour law, Annual leave [大假] can not replace Notice [通知期]. Of course if both of you make a neutral agreement with each other, you can do it. BUT please think about the labour law is more protect EMPLOYEE. Once the employee play a trick, suffer is an EMPLOYER. Take care.