It's mostly jokes and memes, I think. Most of the people don't actually hates Jill. I myself find her path somehow boring compared with others because she's too perfect and her path seems to go on rails (destiny). It's not an emotional rollercoaster like Sage's, Bella's or Quinn's. Also, somehow DPC fucked up her face with the mouth, eyebrows and the makeup. She's sweet and gorgeous when she's serious, but when she smiles she becomes an evil racoon. Hence the memes. But I don't dislike her as a character. She has really cute moments and for sure she cares about MC, maybe more than any other girl. And I can be wrong, but I think most of the people think the same.