Congrats to your wife, on both becoming a citizen and being chosen to give the speech.
In my experience, the secret to public speaking is to say what you have to say and not be concerned with the audience reaction. Communicating your message is the purpose. How it's received by the audience is out of your control so there's no point in worrying about it. Some will love the speech, others hate it, others won't even listen. The point is that at the end, you've said your piece and shared your ideas with those who really do care to listen.
I've had to do some public speaking and it's really easy when you just don't care how the audience reacts.