You must not provide the air ticket. You are not responsible for that. Also you need to ask her sign you a letter to apply the urgent leave and specify the reason. In case she does not show up on report date, it is supposed she terminate the contract herself. Then you can send this letter to immigration in case she really doesn't show up.
Of course I don't want you to be so unlucky as me. However, you also have to prepare it psychologically. The possibility that she lies is really high. Many helper doesn't welcome NB baby. Also you already have 2 daughters. It may be the reason she leaves.