MIL purposely made a negative remark about me on the phone. How should I handle this situation?

Your husband stuck up for you, that's good. Seriously, there's nothing you can do about your MIL's attitude, and really, her calling you "silly" is really not all that bad. I'm just trying to say, it could be a lot worse! Laugh it off and let it go. And be grateful that your hubby is on your side.