I love this series, for me it is the perfect mix of action, fantasy, and romance. 

Inventor, girl genius Tinker lives in a near-future Pittsburgh which now exists mostly in the land of the elves. She runs her salvage business, pays her taxes, and tries to keep the local ambient level of magic down with gadgets of her own design. When a pack of wargs chase an Elven noble into her scrap yard, life as she knows it takes a serious detour. Tinker finds herself taking on the Elfin court, the NSA, the Elfin Interdimensional Agency, technology smugglers and a college-minded Xenobiologist as she tries to stay focused on what’s really important – her first date. Armed with an intelligence the size of a planet, steel toed boots, and a junk yard dog attitude, Tinker is ready to kick butt to get her first kiss.

 Wolf Who Rules finds himself besieged from all sides in this sequel to TINKER. Viceroy and head of the Wind Clan, he had been able to guarantee the safety of everyone in his realm, but faced with an oni invasion, he has had to call in royal troops and relinquish his monopoly of Pittsburgh, which is stranded on Elfhome. He now struggles to keep the peace between the humans, the newly arrived Stone Clan, the royal forces, a set of oni dragons, the half-oni children who see themselves as human, and the tengu trying to escape their oni enslavement.
Meanwhile, Tinker strives to solve the mystery of a growing discontinuity in Turtle Creek. She’s plagued with inexplicable nightmares that may hold the keys to Pittsburgh’s future. The only clue from the Queen’s oracle to help Tinker is a note with five English words on it: Follow the Yellow Brick Road. Oni, and dragons and tengu – oh my!

Elfhome. A world of powerful magic, beautiful elves, man-eating trees, frost-breathing wargs, and god-like dragons. Pittsburgh. A city that has been stranded deep in virgin elfin forest to stave off an invasion by the merciless oni. Its population of sixty thousand humans and a handful of elves are pitted in war that will only end in genocide. Winter is coming. Supplies are running low. All political ties are fraying. Hidden somewhere in Pittsburgh’s crumbling neighborhoods, a vanguard of oni are growing in number and attacking from the shadows.
And children are disappearing.
Girl genius Tinker was once a human orphan, growing up on the Pittsburgh streets. Now she’s an elf princess with all the bells and whistles. She rules over a melting pot of humans, elves, half-oni, and the crow-like tengu. Prejudices are rampant, pitting even the elves against each other. Hoverbike races, concerts of rock and roll fused with elf music, and artist communes of human and elves are proof that Pittsburgh can be a place where races and species can meet and meld in freedom.
Tinker is determined to make her city a place of such freedom. She’s going to have to kick butt and take names. And she has to do it quickly. Seven elf children are already missing — and the oni eat their prisoners when they outlive their usefulness.
Tinker uncovers ancient secrets and a web of betrayal as she searches for the children. The oni will stop at nothing to win, so neither can she. At five foot nothing, Tinker’s greatest weapon has always been her intelligence. Politics, she discovers, is a battle of wits, and she’s heavily armed.

Note: If you want them as e-books, you have to buy them from Baen’s store.   On the other hand, the prices are very reasonable there.