Let's start with the fact that this IS about a princess who is sent off to marry a foreign prince and she can talk to birds and horses and stuff, BUT, it is not a wishy-washy fairytale.
Ani is the Crown Princess in her kingdom, but then her mother replaces her with her brother, because she is worried that the kingdom will not trust a queen who "supposedly" talks to wild animals. She is sent off to a neighbouring kingdom to marry the prince there. As if this wouldn't cause enough problems for poor Ani, during the trip there is a mutiny and her title is taken away by her lady-in-waiting and half of the guards. Suddenly Ani is titeless, and is forced to work as a Goose Girl for the king (hence the title of the book.). Ani is dead set on getting her title back before her lady-in-waiting starts a war between their two kingdoms. On the way, she makes real friends, finds love, and discovers a secret strength that she had no idea she possessed (because, let's face it, she was VERY naive and shallow before).
This story is about independence and bravery, and not doing what you are told just because you are told.
This book keeps you on your toes for the whole time, and just when you think that Ani/Isi is safe... BAM! the bad guys come in and try to murder her in the night.
When I had finished the book, I figured out that it was actually based on one of the lesser known Grimms fairy tales. So I went and read that fairy tale, but I still think this book is better.
When you finish the book, I guarantee you'll be searching for more.