Wow....that's some great news!
As was said by Julie, just tell her up front that you don't know what to say sometimes.
And also remember that she is (for now at least) a complete stranger. Yes, she is your blood relative. But just be careful. Of course all of us want this to go smoothly and end up with you both having the rest of your lives to be brother and sister!
Where does she live? Will you actually get to meet her face to face? This has to be SOOO exciting for you!
CONGRATS!!!