Leaving the country has nothing to do with it, it is all about informing immigration if your status (for which you were issued the extension) changes. If she were on a visa, then that would be totally different, but she is not.
How is it vague? You do your 90 day reports where you have a TM30 filed. If you travel, then the hotel or friend files a TM30, you can then file a 90 day report there, then when you go home, file another TM30 and continue filing 90 day reports at home.