I wasn't going to give this plot another thought but some ideas just popped into my head. They're probably worthless because I suspect anything that arrives so easily is cliche but it may help. In fact, 90% of everything is just reworked cliche so maybe you can make this work if you twist the formula enough.
Rather than making it an art school run like a prison, make it a insane asylum run like an art school. The story takes place in a post-collapse dystopian future and Penny is a ward of the state who keeps coming back to the nuthouse because she has nowhere else to go until she can graduate and prove she's not insane. The main form of therapy at the nuthouse is some cheesy art therapy because the guy who runs it isn't a real shrink but some moron puffed up on self-help books and art therapy. He's like a combination of Dr. Phil and Hitler (remember Hitler was an artist who said anyone who paints the grass blue and the sky green should be killed and Dr. Phil and Hitler have the same mustache and like to scream at people). Also make this guy a fan of mainstream art, empty pop culture and old Victorian gothic novels so we see that his whole "art therapy" depends upon either making Penny into a member of the mainstream or making her act out her illness like a gothic heroine (because that sort of emotionally disturbed female is the only type he understands). This gives you room to indulge in all the cliches of those things while being able to claim it as parody.
Scrap the idea that Penny was put into the nuthouse after some sort of collapse and change in her art. Simply say that she grew up there because she's a ward of the state with nobody to take her. This would also make her rebellion seem more authentic since it comes from within and comes spontaneously without outside influences. Penny's art and rebellion reveal that there is something wrong with the school's methods, which have not been questioned until now. What makes it worse is that people who graduate from the school tend to come back as teachers, thus reinforcing the same bogus concepts (shades of Bronte's Jane Eyre!) Other students either become brainwashed to the teacher's POV or merely fake it by painting some bland mainstream still lifes to get out of the place but Penny refuses to do that.
Make the janitor a male instead of female and make him a parody of the friendly janitor in The Breakfast Club and the rebellious janitor in Nirvana's Smells Like Teen Spirit video. Read
Cobain's journals where he developed the character of the rebellious old man who secretly sympathizes with the punk rockers in the video (something that was cut from the final version).
It's still cliche after these changes, but now you can play the parody aspect anytime it seems too predictable. I suspect this angle had already occured to you merely because you named the character Penny Dreadful.
BTW: You owe me 15% since I'm a writer and all. Muahahaha!!
