I don't think Yukari is actually all that edgy. I think she represents fear of the unknown and understands that this fear is at the core of a youkai's power, so she deliberately feeds the mystery surrounding her.
For this reason I don't think she's as powerful as she tries to appear, either. Fear of the unknown is like an illusion. As long as it's maintained it's very powerful, but once the unknown is no longer the unknown the observer generally realizes there's nothing to fear, and that there never was anything to fear in the first place. That's basically why youkai started to go extinct in the real world.
She's capable, definitely, but her behavior betrays a kind of fragility, I think.