I only remember reading it as a child, so not sure if it was published in 90's or 2000's. In it, a girl is aware of mythological creatures and people who feel an affinity to them, such as banshees, unicorns, harpies or kraken. Each kind of creature is assigned an element, so kraken is water, harpies are air, dragons are fire etc. The girl thinks she discovers her creature and the medium society leaves it at that, but then she discovers she has affinity to another creature, then another, then she finds out she's this universal medium for all kinds of mythological creatures.
There's a big baddy who wants her for her powers, but I can't remember his ultimate goal.
Anyone remember reading anything similar? Cheers.