Is There an Easy Way to Learn Sign Language?

I think that's a wonderful idea, and will mean a lot to her. First, you should know that the sign language most Deaf people use (in the US) is American Sign Language (ASL). Schools have been using a system for showing English on the hands, called SEE (Signing Exact English), but it's not what most Deaf people use unless they're forced to in school. So head to the library for a book and some DVDs, but be sure they are ASL guides. You can also check your local community center or community college to see if there are classes you can take, at least to get you started. Signing involves hand shape, movement, orientation, and more, so it's good to get the basics down correctly. There are also some good websites that show you how to make the signs (I've listed one below).

Your sister will become your best teacher, but if you can learn some to start with it would be a real gift to her. Good luck, and enjoy! ASL is a lot of fun (and maybe you can become an interpreter someday — it's a great job).