She could try laying paper towels over the stain, and running a warm clothes iron over the top, much like you would do for wax in carpet, but she may not get all the stain out of new concrete. Time and mother nature will help, it should be less visible after weather has helped to degrade the wax.

Here is a link that might be useful: spilled wax removal porous surface

The stain was probably caused by oil. Maybe she could try covering the stain with a shallow layer of detergent, then spraying it off? That's how my mother used to get car oil stains off the concrete garage floor. Good luck!