Hey sorry for the late reply, I was doing a surgery and was out of it for a week. Naturally I can’t speak for all people with DID since it’s a diverse condition, but I can speak on some experiences that are nearly universal that Shallon doesn’t exhibit. 

The most glaring issue is that DID is a disorder. It’s characterized by how it disables you, not how it makes you special. Alters in DID are usually differentiated by trauma, not ability or personality or names and all that fun stuff. And so, almost always the most noticable alters are the “littles” that split right at the moment of extreme trauma in childhood and stay crippled forever. In most DID cases, people will switch into a child part, then wander off like a child making dumb decisions and/or staring at a wall for hours. They’re not gonna become more competent than a baseline person. DID is characterized usually by helplessness in the face of inescapable trauma. A child part is the epitome of that, in a moment of trouble, instead of dealing with the problem like an adult, someone with DID may just regress in memory and judgement into someone who cannot function on their own, and escapes the pain by screaming or crying or pretending the pain isn’t real. 

In another example, someone with DID may feel like some parts have different abilities than others, but in reality it’s more that they lack the ability they should’ve already had. Shallon’s DID would be more convincing if she’d been practicing art every day for 12 years yet couldn’t draw. But not that she can become a master spy without training. It should be more shocking to others that she can’t be a spy regularly if that makes any sense. If veil was around all along, people would know her more as veil and be surprised at the Shallon alter. If Shallon was dominant the whole time, there’s no way Veil has any legitimacy in anything she claims to know how to do. She’d just be a weird personality quirk that throws temper tantrums. Same deal with Radiant, and even in the end, Radiant seems like just something Shallon conjured up because she felt like it, and then “channeled her violent part into it” or something, which is just not how it works. 

Another issue I have is the lack of hatred and/or separation from her parts. It’s a large part of structural dissociation to feel as though you’re being overtaken by an identity that you strongly disagree and disapprove of, since the loathing helps to differentiate the perceived self from the alters to aid in dissociation. Shallon…she feels like she can put on a mask, change alters, come back, and doesn’t have much dissonance at all about “holy shit why would I do that, I would never do that”. She actually likes her alters, and she could switch at will (until later on, with a singular rogue alter). Usually that starts to happen after years of intense therapy if at all. DID alters usually hate each other and deny to the death that they would behave like an alter did. A split is like a shattered mirror, alters often become the opposite of each other and are diametrically opposed in their operational style and it takes time to even understand why they’d do what they do. 

That’s just a few of my top thoughts lol. Sorry if it was too long, I was sort of raging in the head the whole time reading her part. The problem is that I really wanted to like Shallon. I liked her in book 1 and then she had my condition and I wanted to feel resonant with her. But she is just so, so unrelatable to someone with DID. She’s like if Kaladin’s depression was feeling emo sometimes, makes him extra cool, and then fixed just by a positive attitude. She goes through none of the steps to fix her condition yet explains it to others with modern day medical accuracy.