If I was in your shoes, I'd just have them pick one up there. For my stint in Trinidad, we picked up prepaid phones when we landed there. The plans were all jacked up, and it was actually cheaper for me to use a Trini cell phone and call the USA, than it was for me to call a land line on the same island. If they get a prepaid phone with a chip, you can bring it home and save the phone for the next international trip. My phone down there was basic and only cost like $20.
Another option is to hit up eBay, and get something thats Unlocked. Look for an AT&T or Tmobile phone, so they will have a chip. Then they can just pick up a sim card when they hit Brazil.
Or my preferred way-Skype. Free to download and install on your computer. If you put it on a home computer, you can call Skype-to-Skype for free. You can use webcams, or just a mic. For $3 a month (and you can just get one month) you can buy unlimited minutes to the USA. So download it on their laptop, buy that plan, and they can call your cell phone, or her friends, for just that $3. Of course, that relies on them staying somewhere with high speed.