I'm guessing plus sized means they wear clothes that are positive in value i.e. larger than size 0. Otherwise.
Turns out, she's a size 10 (US). She's also 5'11". Name: Myla Dalbesio
There appears to be a lot of controversy about this, but she was never explicitly referred to as a plus size model. She's called herself an inbetweenie, not skinny enough to be a "normal" model but not large enough to be called plus-size. She was mostly just the first such person to advertise CK, but CK never actually gave any designation on her size. Which, honestly, is actually GREAT. I'm glad CK never categorized her, didn't say to the world, "hey look, we have normal women too!" Rather, they just put the photos out there, and that's it. We don't need to know it's a photo shoot of a plus size, or inbetweenie, just that it's a modeling job and she's the one they used.
But at 5'11", a size 10 is about goddamn perfect. She's gorgeous. Wonderful body size ratios. But that's because she's just, I hesitate to say it, "a big girl." She's not big like plus size, but with her height, she's more Amazonian Princess than anything: a full figure tall frame. Outside of her height, she's much closer to the average woman (said to be a size 12 in the US). She's normal, not stupid thin but no body rolls either. At her height, she fills out the dimensions differently than a size 10 (UK size 14?), and does so gorgeously.
Google her and you'll find numerous examples of her beautiful figure. Oh, and you'll also find that she likes to apparently keep a little bit of a bush, so... google wisely, at home, as it's likely NSFW unless you trust your google image filtering. lol