you may consider
1. a small B/D cake, she can blow the candles with your kid(s), take some pictures, get them printed so she can mail the photos to her family
2. buy her handcream / handbag / anything you want
I have celebrated my maid's birthday as follows:
1) try to find out what she likes or what she needs. I bought her a thick coat since her birthday is in winter which suits her well as she needs this. I think a well thought gift is better than money.
2) bought a rose on behalf of my baby
3) bought a small birthday cake
4) bought her out for dinner
5) took a photo with her.
She (ex-maid) has only worked for me half year. At that time, her performance is just so so. But I hope she will be happy as her family cannot come here to celebrate birthday with her.