E.D.
I think cash is an excellent idea. I have heard a weeks' pay as well. I mean, she is caring for your most prized possession. But I do like the idea of a gift card that can be used at more than one place, like an Amex Gift card. And a framed picture of your child and her. Something like that.
Really, I am sure she will appreciate whatever you do! Think of how you like to be appreciated and appreciate her the same way...
Hugs,
E.