I'm thinking ISFP, lol. I'm not sure... her face expression kind of reminds me of my mom's and my cousin's, and they're both ISFPs. Plus, she seems grounded and she seems like an introvert... and she talks about what SHE wants and stuff. SO yeah xD
I think she is ENFJ, just like Jessi J. Those kind of people are emotionally led people but they are extremely driven and ambitious. The fact she was a 'huge' diva backstage on the X Factor and often caused tantrums leads me to believe she has a very outspoken and controlling personality.
She remains chilled in interviews but there is a fire burning inside her ready to erupt. I can always spot someone with a temper when I see one.