I mean, sure, but it's not a rule we have to follow.
The obvious decision would be the patient, I thought of it too (you can even see it in my AI generated image from my post earlier, a mask and chains were in the prompt with that intention), but taking the route of something people don't generally think about, such as the nurse, would Subvert Expectations™, and give people pause to think about the connection; even if it's for a split second, that time thinking about it would make that image more memorable, and in the future, recognizable. It would also have the viewer to think about why a mascot, who is usually presented as positive and cheerful, would be in such a dilapidated state, and if they inquire on the backstory of her naive world view being shattered, it can establish a sense of connection and relatability, further cementing the mascot in their head.
I think the nurse would be better for marketing and recognizably; in addition we can, if we want to, put her in a lot of interesting situations in ads or as a local site comic.
I don't know how the patient route would be. Would she be overly cheerful? Overly angry? Deadpan? It's not that we can't do anything with it, but it would be very predictable and much more difficult to flesh out her personality as her character would have to be within the prerequisite of being insane; if she's institutionalized, then she's probably not very stable, so her character and emotions would likely be in the confines of being in the extremes, which starts to get clichéd.
I'm all ears for fun and interesting ideas for the patient, as I can't really think of any.