If she has worked for you the entire time, I would suggest the following:

1. If she wishes to stay, find a good, suitable family for her.

2. One month's salary for each year she has worked for you up to two years. This is typical severance for expats in higher end jobs, and I don't see why it should not be the case for your maid.

3. Tell her that you plan to provide her this on condition that she continues to perform her duties to your expectations until you leave.

4. If she does a great job after that, I'd through in an extra thousand as a gratuity.