I think it's a great choice. She really has nothing to lose. It's something different from her, and even if it doesn't do well, radio isn't going to just stop playing her completely because of one under-performing song. I mean, look at Rihanna, she had multiple flops in a row and her new single is doing well.
I think they are saving it b/c the competition is to strong it will get lost in rotation
Wide Awake is the perfect ending song for the TD era. She also says shes planning on releasing a new album later this year so I'm going to guess this is her last single. She's going to need a break before embarking on a new era.