I don't think she would sell out stadiums at all. Also, stadiums really show off a person's voice due to their size. I think a stadium would completely swallow her up as she doesn't have a great voice anyway. The only ones who I think could sell out stadiums are Beyonce (she's a touring artist now and her Super Bowl performance proved that she would absolutely kill a stadium concert), Taylor Swift (I don't get the fuss over her, but her fan bar is gigantic). Also, I'm not a fan of her but I think Madonna also could. I know she's failed to sell out concerts recently but I think that's due to the bad organisation of the tour/tickets and the fact that her tickets are so expensive...if she sorted that out she'd be fine I think. Beyonce I think will be the next to do stadiums...she's already tested the waters with stadium concerts such as Chime For Change which involved other artists too but it was obvious most were there to see her! Super Bowl proved she can pull of stadiums and when she performed at Glastonbury she had 175,000 people watching her set. I reckon on her next tour she will do arenas but will add a few stadiums too...that's the smart thing to do to begin with. Oh, also her and Jay z recently performed in stadiums on their joint tour...although it would have been two fan bases, it was a good way to test the water and it definitely worked.