It looks to me like the second path (C:\Users\Brent\Documents\Arduino\libraries\SmartThings) would be the correct one, since it’s important that the folder matches the name of the SmartThings.cpp and SmartThings.h files it contains and is top level (I believe). After that, have you tried quitting the Arduino IDE? That’s what the problem usually ends up being for me.
I actually got this working. The problem was that the zip file I downloaded had illegal characters in it when I tried to import it into the Arduino app. I changed the file name(took out spaces) and imported and it worked fine.
This worked for me too. Good call. For others, makes sure you pull the space out of all of the files. I think there were three different "Shield Library"s.