When I sacked my maids in the past, I always buy an actual single ticket to PH, but have to be open since she has the right to remain in HK for up to 2 weeks, and give the ticket to her together with the termination letter. You also need to give her $100 for travel to airport. Ask her to sign a receipt for all these things. Never give money in lieu of an air ticket as she will have money to stay in HK and seek revenge against you. Don't forget to have new locks fitted as soon as she has left.