What's sad is that people who weigh more than her (a lot of people) are looking at that statement and it's making them feel bad/worse about themselves than they already do.
And this is promoting "positive body image"
I think when they say plus sized, they mean over size twelve or somethin like that. Based on those parameters, you can have any level of fat on you body, it is based in this case on her height and bone width.
I realize I'm a year late to this party, but I felt someone should share knowledge with y'all. She very well could be a true plus sized model, because your clothing size is determined not solely on ones waist. If that were true I'd be a size 0 and an extra small not a size 7 and a large. Furthermore you might argue that she isn't promoting a plus sized positive but she is she's just promoting it for a different body type than some of the female whales who wish to have their fat rolls displayed in glory.
And this is promoting "positive body image"