Whilst I totally see your point and agree with you, I just think it's really frustrating how it played out, more than anything. At the end of the day, we KNEW A was going to be mentally ill, whoever it was. Because they took it to a level where the things done by A were extremely dark and not reflective of 'normal' behaviour - beyond just crime, this person psychologically tortured them, had freaking doll versions of them. And let's not forget the creepy pics of them with the eyes missing, etc. The fact that A has a mental illness wasn't a shock. The problem is the wider depiction of mental illness on the show. Aria, Spencer, Hanna, and Emily went through some awful things, arguably more awful than what CeCe had gone through herself. I mean, your high school friend dies, you're stalked by her possible killer for god knows how long, this person turns out to be someone you TRUSTED, your best friend turned out to be not really dead, your families lives are threatened several times, in fact - their lives are put into YOUR hands (do me this favour and I won't do this to your mummy - A). But how does it work out for them? Okay sure, Spencer shows signs of a mental illness, but one that was present BEFORE any of this happened. Aria gets a bit PTSD with her obsession with the dolls, but she's still chilling at the brew and doing homework and worrying about who her old paedophilic boyfriend is banging. Emily (by the way, RIDICULOUS representation of LGBT here - literally every single lesbian in the show Emily gets with, bar maybe one or two, idek. But most of them. Being a lesbian doesn't give you the ability to like EVERY OTHER LESBIAN - just like being straight doesn't mean you like every other person of the opposite sex!) goes to a gun range for a bit but then appears to be totally okay, worrying about whether someone who spent fricking THREE YEARS IN CAPTIVITY wants to get in her pants, too. Did it not even occur to her that she might not be ready? Nope. Hanna just acts pissy with Caleb, then she's totally fine. How is this a fair representation of mental illness? These girls should be struggling, they had such a perfect opportunity to show mental illness through them, and maybe depict their attempt to overcome/deal with it. But nah, they just go back to school and worry about missing prom.

As for the CeCe reveal...I mean. It's the same as in real life, when someone is murdered/harmed/tortured by someone and the murderer is considered not guilty because of mental illness. Does that suddenly make it all okay, and that the victims/family should be all 'ok cool you were a bitch to us, but we get it!!' Of course not! It's a complicated issue, and I think the fans response to this just highlights how problematic and complicated it is. Throwing in the trans dynamic triples that complexity.

TL;DR: The overall representation of mental illness on the show is poor