Is it normal for my 16-year-old daughter to want to dye her hair blue?

At 16, blue hair is practically the bare minimum you can expect, it's an age where everyone wants to assert their own identity and hair color is one of the simplest (and reversible!) ways to do it! Let her do it, in a few months she might change her mind anyway.

It's totally normal, and anyone who says it isn't probably just doesn't remember what it was like to be 16. Here's a practical tip: before she goes for a permanent blue dye job, have her try a washable color spray for a couple of weeks first, so she can figure out if she actually likes it or if it's just a passing phase.