Christmas gift for caseworker?

Ok here I am again with another gift giving question. Please excuse my lack of knowledge on the subject. Is it appropriate to purchase a gift for our adoption caseworker? She is a big part of our lives and we are so thankful for her role in helping us to become parents to our boys. I am unsure about the gift thing because she is a government worker. Please advise and also if you are giving your caseworker a gift, what is it? thanks Kathy