Shorts are so vastly different in so many ways that she really needs to try them on. The most critical research is in the fit.
How many miles does she expect to ride at a time? There is a significant difference in the chamois, fabric and construction from price range to price range. At $40 you may only get shorts that are comfy for an hour's ride or a spin class.
Also, on a road bike, loose the shell. It will only be one more layer of wrinkles and chafing opportunities.