Read this book a few years ago, it was a trilogy, the last of which was released sometime between 2008-2016. Female author I think.
Main character is a girl, in maybe her 20s, a witch of some kind, but she has to keep that a secret, because there are supposed to be no witches left.
The main conflict is these giant, flying, hypnotising dragonfly-like creatures, that started terrorising the land. If you look directly at them you are hypnotised and can't move and then they kill you.
There are a series of pillars in the northern region of the land, which everyone hates to go near, which used to keep out these dragonfly things, the pillars are decaying, hence why the dragonflies are getting through.
The pillars were supposedly made by the witches, who sacrificed themselves to make them, but in the last book it turns out all the witches were forced to do it against their will.
(It's not The Pillars of the World by Anne Bishop).