So, most of the episodes are fairly benign aside from the mature language and themes.

Spoilers

However, the later episodes get graphic, including two graphic rape scenes (there is no nudity aside from butt shots if that makes a difference) and a graphic suicide scene. That said, I'm in the camp that the graphic suicide scene is disturbing for the "right" reasons: to shock you and make you realize how horrible it is. But others say it glorifies the suicide by showing it on screen, and I can totally see how one might think that.

Again, I advocate for not judging a child's ability to handle mature content based on their age, and more on their maturity. I personally wouldn't recommend a suicidal person watches this show, because while the show's intentions are good in getting people to talk about suicide and bullying, the way it executes everything portrays suicide as a sort of "revenge karmic justice tale", and that does "glorify" it in a sense in my opinion.

Personally, I probably wouldn't go out of my way to watch with a 9 year old with "typical" maturity levels watch this show. But if you feel as though your daughter can handle a few disturbing scenes and a show dealing with mature themes, go for it. I personally would've felt fine with my boy watching at 9 with parental guidance were it not for his past abuse putting him at risk for being triggered, but again he's always been mature for his age.

I would suggest watching the show without your daughter first, than making a judgement call. If you decide to let her watch it, I'd watch it with her to help her through the more disturbing parts.

Spoilers

In case you want to know what episodes the graphic scenes are (and what they are), they are episodes 9 and 12 (rape scenes) and 13 (suicide). There are trigger warnings before these episodes, but these scenes are very difficult to watch.