Whalen's 3pt attempts were down in 2012 as well, before the arc was moved out. The 2012 season just happened to be when the Lynx drafted a kid who could shoot threes pretty well. I think this kid's name is Maya Moore.
The presence of Moore doesn't explain why in the 2013 season Whalen took by far more shots than in any season she's played in the WNBA (407), while remarkably only 9 were considered 3 pointers. Many of her perimeter jump shots that season would have been 3-pointers the year before. She wasn't a particularly good 3-point shooter to begin with, so there was no point in moving even farther away from the basket.
Despite the presence of Moore, the Lynx were determined to improve their three-point shooting heading in to last season and made use of a tool that tells players the angle of their shots. Whalen's confidence improved enough that, despite missing 12 games due to injury, she attempted almost as many three-pointers as in the previous 3 seasons combined.