To hate is basically hold a strong dislike for whatever it is that is being hated. By "dishing" on female celebrities Bella Thorne is showing that she has at least some level of contempt for them. This shows an inclantation to hate or be a hater. The difficult part of this question would be, is the status of being a hater of this topic a bad or good thing.
Bella Thorne is obviously a hater. Anyone that spends their time dishing it out on Hollywood celebrities is obviously a hater to some degree. The fact that she dishes on other females further proves that she is a hater. Females in Hollywood or not, need to stick together and take care of each other.
Bella Thorne is definitely a hater when you look at how much gossip she dishes on female celebrities in Hollywood. Bella Thorne can't keep her mouth shut about other celebrities, while those celebrities typically say nothing gossip-y about Bella Thorne herself. Bella just wants attention, because she's a complete and total hater.
She might not like the other female celeb, which could be due to a personality conflict or other event. We don't know about prior interations with that person. Therefore, I wouldn't label her a "hater" unless it happens on a consistent basis and she seems to be targeting other female celebs.