Dorothy is a sincere and well-informed climate activist. After being arrested at a protest, she's laid off from her political writing job for a mainstream, corporate kind of Democrat. Dorothy is more authentic, passionate and overall more leftist than the people she's been working for and clearly doesn't belong in corporate mainstream politics. So...she moves back to her childhood home, a small town in Texas, because she thinks her talents are being wasted where she is. How she comes to this conclusion is a bit sketchy, BUT in reality a lot of liberal Americans with the financial ability to do so have moved to Red and "Purple" states to try to liberalize the culture there away from a Republican stranglehold. Presumably, this is Dorothy's goal.
Instead she embarks on a campaign as a faux Republican because she finds a state loophole in Texas that would allow the Dem candidate to win if she wins as a Republican and withdraws at the last second. Obviously, it's something so hair-brained that it could only be the plot of a fictional movie. Over the course of The Hater, Dorothy learns that the women in her town, at least, aren't actually homophobic, hateful or pro-life. Instead she discovers kind, genuine people who are locked into some kind of conservative nightmare who would break free from that view given half a chance.
I think there's some truth to that reasoning, especially with wives of conservative men in Red states having been pressured to vote Republican just because their husband does. The movie makes it's point, but its done in a clumsy and unrealistic way. I enjoyed the first half of the film more so than the second, especially the end.