The things Solipsist was saying that are just going to take up too much real estate if I actually paste them in here and are within spitting distance of this anyway
I feel like a broken record having to point out the "Our X Are Different" series of tropes all the time on this site. But,
Our Vampires Are Different is a thing. We pretty much just know that this vampire girl can survive off of tomato juice and turns to ash in sunlight without dying permanently.
Also, "the manga made no attempt to point us towards that direction" bit in particular. It made no attempt to point us towards her being older than like 13-15 either, but here you've been assuming she's at minimum 18 if not older than most of the adults in the cast by decades or centuries, because vampire. But again, "Our Vampires Are Different" kind of means anything goes depending on what the author wants to do. Anything but her personality, drinking tomato juice, turning to ash in sunlight, can go in any direction from here. We can make predictions based on the vampires we're all familiar with but that's all they are, predictions. The author can and may throw curveballs at us because they do that often enough to make a trope out of it.