She's a public figure, there will always be hate.
She just needs to learn that, there are many other celebs who get WAY more and worse criticism for their red carpet looks than her tbh.
I agree that her style is boring as hell, and I'm not very fond of her, but I actually feel bad. Sucks that she's sensitive, because that means she'll never truly be happy in Hollywood. Artists will always be criticized for anything they do, I mean Selena had to deal with similar insults (especially body-shaming) for a large part of her career.
Ariana sis, do whatever you please. It's your body after all. But she really needs to toughen up and learn to ignore or leave the show-biz to someone more capable.