I think that people aren't barbaric and don't just chuck mental into an asylum forever. Such a mental illness would have therapy, assistance, treatment. Not just being launched into a dark hole forever. So, maybe at worst she is put on the sidelines for several weeks/months as she recovers, but not vanished forever. But, I was more in the mind of active assistance, in the school, helping her over come it while still keeping her around.
Let me speak with you further.
First, making a violent character isn't generic, unless you make it so. Just because it is a common trait people write into characters, doesn't mean it's boring. Making Mokuren randomly go into the corner nibbling on nothing absolutely BREAKS her quiet and (actually already...) violent character. Yeah your character is already violent, go the whole way.
But again, it's only generic if you make it so. There are many ways you can make it have more depth than simply someone who lacks the inhibitions to attack another person. For instance violence was perhaps the only thing she knew until recently, and as a result is now seeking to change this and put herself under better control. Maybe she's violent because of a strong sense of justice, that justice should be paid in blood, and that soon she will see that violence isn't the only answer.
You need to think about your character's moral compass if you want to make an interesting character. Change, or seeking change, also makes an interesting character, because it's development that readers can gauge. So again, a violent character isn't boring unless you write it that way. Just because it appears to have been done many times, does not make it a bad thing. I'll give you some examples in RWBY itself.
Weiss is a rich girl who is somewhat snobby. Oh I think I've seen this in... Most animes these days?
Yang is a spunky popular girl. I think she's in just as many animes as Weiss' character is.
Jeanne is actually a combination of two. Though he exhibits mostly 'main character' traits, like hidden potential and rising to the challenge when the need arises, especially when close friends are involved. At the same time he is the butt end of some jokes like the... Main character's close friend.
Our Silver guy who kicks, and his partner, are very very obviously the strong cool villains we see in most fighting or combat animes and even shows, and Roman is like a British Joker. Absolute balls at combat, but he's kind of a mastermind. I just wish they wrote his plans better, because it all just looks like a bloody gambit and asspull sometimes.
This is something people don't seem to understand these days. It's all about execution now. It is incredibly difficult if not impossible to make an original concept now. You should take concepts that are already used, and explore them in new and different ways, or try it in a way that may be interesting, rather than immediately dismissing it as 'boring'.
Next off, I know people with mental illnesses, one of which is my cousin. Literally the only thing stopping him from being put into an asylum is family, and because his affliction isn't so bad. At the very least he does not seek harm upon others. If there was a mental affliction where the patient sought to harm others or themselves, I guarantee you they would be put under the highest amount of scrutiny depending on the severity.
But in any case, tell me why you think she should have this cannibalism? I will say that it is probably okay, as long as she is actively seeking help, if you choose this route. Ozpin must be knowledgeable about your condition, for obvious reasons will be kept secret from anyone else, but your actions will not be met without consequences if you choose to eat another person. Whether or not Mokuren reaches out to anyone on her team or other people, will be entirely up to your character.