Check the links at the top of this forum. I think there is info on this topic. You should be able to find help training your dog to get certified - which you will probably need to do, if you want to bring her into stores and such.

But don't worry about the training. Chihuahuas are brilliant dogs and yours will probably learn what is required quite easily - and I bet she loves having a job to do.

Good luck and let us know how it works out for you.