if she is using iOS 5 or greater, she can also use the free apple text on the iPad but only to communicate with other iOS 5 devices. or in other words, not with another type of phone besides an iPhone.
That being said, there is an app for that, and here is one of many..:
Free Texting with the iPad Wi-Fi and iPad 3G | Text Apps Designed for the iPhone: Textfree | Que