Nearly every article about female celebrities, particularly those who are actresses, calls them "whip smart" at some point. It's in the same vein as celebrities "flaunting" their pregnancies - usually by walking down the street and being papped by someone hidden behind a bin. Or, and this is my favourite, "oozing style" by wearing clothes.
All of it is meaningless in any real sense, it's just what journalists say, and they say it about everyone.
I'm not saying Meghan isn't smart, i have no idea, just that the magazine is following established norms by saying that about her.