Well there are a few hundred different species of dianthus--some are much better suited for the task at hand here!
Maybe if you can find the tight hummock producing types you might want to suggest she give one a try. They aren't exactly
spectacular in the spring or the summer, but, I really like the green mounds in the rocks--like this one
We get plenty hot here, high nineties--low hundreds, and many of them do well here
