She is beautiful, and it is a beautiful photo. She is wearing shorts and more coverage than many women do at the beach---and as a woman, I know that many women who wear bikinis at beaches do not think that they are sexy, but rather just want to wear a bikini and realize that they do not have perfect bodies. Bikinis are a) more comfortable than one-piece suits, because they do not pull on your shoulders or weigh down on your chest and b) allow more tanning, which covers up imperfections in the skin, such as age spots and freckles.
This is very clearly an art photo. There are very few people who would be offended by this. She is modest in her dress (for an art pose) and also in her posture. Perhaps you have never seen a provocative picture? Women can pose quite a bit more seductively than this.
Also, her art is free for DeviantArt reference use. She is not making money off of this.
Finally, she is beautiful, so why shouldn't she be a model? She has an amazing waist, lovely curves, and a beautiful, feminine face. Allowing people to view her belly (which has been socially acceptable since the 1940's in the US, and is present in many forms of art from the Renaissance and before) gives artists using her as a reference to see the unique and graceful curves of her stomach, should they care to draw an image which presents a female's belly.
anatomy... it's for the study of anatomy...
so every class that has a nude person posing to be studied and drawn is solely to arouse the students???
welp, it outta be a good semester!!! xD