I actually think this could be a smart move for them.
There are millions of American women who will identify better with her than with the typical supermodel / actress / celebrity on the cover.
When these women see her on the cover when they are in line at the supermarket in the next few weeks, they'll be inclined to pick up the magazine and maybe even buy it.
Next month, the ad sales force at Elle tells their advertisers that circulation & readership have grown, and can charge more money for the placements.