N.D.
Marie's suggestion was fantastic! I haven't been a Nanny but I think a scrapbook/ photo albulm of the past two years would be a nice send-off. Another nice touch could be to send the Nanny and your daughter to have professional pictures taken. Pictures mean so much and I am a true advocate of using them to commemorate things. In addition, you can use pictures to make gifts. Walgreens.com is where I have a lot of my picture gifts made. They can do anything from coasters to afghans- you might consider this too!
Good luck. I would be curious to hear what you end up doing. Sorry to hear that you are losing your much-loved Nanny. Sounds like you could use her again with a baby on the way.