I would venture to say that Carrie appears to be a very *young* 21 years of age (while Mikalah was a very old - or, rather, precocious - 16-year-old), which would account at least partly for her lack of stage presence. She looks very stiff when compared with seasoned performers like Constantine and Bo. But she's easily the best vocalist in the group (I might even go so far as to say she's the best vocalist AI has ever seen). She falls short as far as confidence and experience goes, which she will gain as the weeks go by.
Along with her huge raw talent, I think her lack of guile makes her attractive to the AI audience. It's obviously preferable to Mikalah's style, which turned off enough people to land her in the bottom 2 the first week, and voted out the second.