I agree that Daisy didn't handle things well. She had every right to an outlet for her frustrations with Aza but not in a public forum where Aza might have been recognized by people they both knew, since the fanfic was popular.

I don't hate Daisy, especially since she was still mostly present and supportive of Aza throughout, with the daily ins-and-outs of OCD.

I don't hate Aza either though. In my own life, I am the Problem Friend with mental illness. No matter how difficult it is to love someone with mental illness, it's probably more difficult to be the one with the mental illness. Speaking from my own experience, people with mental illness know they might make life hard for other people and they feel extreme shame about it, even if they don't (or can't) show it or make attempts to fix it. But still, the loved ones have every right to feel exhausted.

Knowing the author's background (he has OCD) and themes of his previous books (i.e. "Everyone is complicated"), I think we're meant to feel complicated about both characters, just like they feel complicated about each other.