Anywhere from $200-two week's pay depending on whatever you feel should be factored in. One week pay is a not-uncommon Christmas bonus but it isn't the only way. If you want to give more but don't have the money, offering her some extra PTO is a great way to supplement!

Give her whatever you feel she deserves.
Typically a weeks pay seems to be standard.
Gift cards are nice too

We have had our nanny a year. What do we give her for xmas bonus?