Shokuhou's whole appearance is a mystery in general, not just her looking highly mature for her age.
She's blonde but it's never stated that she dyes her hair (which would be against Tokiwadai's ban on cosmetics) or that she isn't Asian, which the novels typically do when establishing hair or eye color (Hamazura, Tsuchimikado, Aogami Pierce, and Kakine's hair are all described as dyed, for example). You can't apply the anime logic of Japanese characters having strange hair colors for artistic purposes since she's consistently and repeatedly referred to as honey blonde throughout the novels (in a constrasting example, Komoe-sensei is drawn with pink hair but the narrative never refers to her having pink hair). The logic of her being a European given a Japanese name possibly due to being a Child Error doesn't really apply because they would have brought up her not being ethnically Japanese. Though to be fair, Hokaze is consistently referred to as a platinum blonde, however she's most likely mixed-race since her father is a wealthy international businessman. Shokuhou's family is never brought up, and one thing that really stood out to me in Biohacker SS is that Mitsuari, a character that is a dark reflection of Shokuhou, talks about her parents multiple times, which feels like a deliberate and direct narrative constrast with Shokuhou. Shokuhou never gives the impression of coming from a wealth like most Tokiwadai students as well. I do find the idea of all three female Level 5s being rich girls funny though.
Despite her probably being the Level 5 which we've the most information regarding her past shown, she's still very mysterious in terms of who exactly she is.
Shokuhou's eye stars seems to be related to Mental Out despite her saying in one line in the Railgun manga that she's had eyes like that since birth, which just makes it more confusing, since she wasn't born with Mental Out. These eye stars are never actually referred to in the text of the novels, afaik. Mitsuari Ayu notably has a
similar eye effect in the Astral Buddy manga however it is many tiny stars instead of a singular one in each eye, probably a reference to their powers being originally identical.
Science-side characters as a general rule have fairly grounded designs which contrast with the utterly ridiculous and alien appearance of Magic-Side characters, and when a Science-side character is unusual-looking, like in the case of Accelerator, it's meant to be significant. Which is why Shokuhou's flashy and bizarre appearance is so strange. Oh, and I also forgot about her weird unexplained verbal tick of calling everything an ability.
It should be noted that
originally Shokuhou's design was going to be much more mundane looking. She was supposed to look like a girl you could easily miss in a crowd (a trait Shokuhou still has despite that btw). This design later got reused to become Mitsuari Ayu, which thematically matches the idea of Mitsuari being someone who failed to become Shoukuhou.
Shokuhou quite seriously sees Kamijou as her personal savior. Weirdly enough she's most similar to Accelerator in how she reveres Kamijou as some sort of exceptional hero that transcends reason and will selflessly save others, which is exactly the sort of thing Kamijou dislikes being seen as. It would also damage a lot of the weight of the Mental Out Arc in Volume NT11 if he were save her at this point in the timeline.