To preface this, I already know the abridged version of what all happens in the story, and I also know what the internet thinks of Ava. So I wanted to play it for myself and see if I can find these so called unforgivable sins the character does. I'm up to Eden-9 (rescue Jakobs planet, right after Maya gets merced), and I haven't really seen anything Ava does as offensively bad yet, and I feel everyone hasn't done anything out of character.
So essentially from what I've played so far, she hasn't really done anything deserving of hate yet.
The Ava hate is absolutely unwarranted imo. I thought she fit right in with the rest of the zaniness of the character roster.
Her DLC missions are basically her starting a podcast and you help her and that's when her character really develops imo. You get to know her a lot more. Also her reaction to Maya dying is good character development too.
E: Maybe flip that. Her reaction to Maya is probably when her character shines and her podcast helps flesh her out.