I think Shion is the least surprising graduation. She was barely hanging on and probably was ready to move on to another chapter of her life, beyond just not being able to handle the stress that went with being with Cover at this point.
She also might be the closest one we've come to that was has some family pressure that amounts to "find a man, I'm not getting grandkids this way!". That's the subtext to the "not a real job" aspect. VA work is a proper job in Japan, so, unless Shion is from an upper crust family, there's probably a little more to it all. She's also been doing this for year and is like 25? It was probably time.
All the best to the best to her and all she does.