Well I don't know how to categorise this - I just know that I loved it, so much that I bought the second and third books and read all three over the course of two days!
The best part is that the first book is free on Amazon for Kindle users (in the UK at least).
The blurb:Gemma Hart never knows when her father is going to whisk her back in time. Her toes start tingling and she has a few minutes to find a secret haven where she can disintegrate and appear in another time and place. While “across the line,” her training and skills are put to the test as she completes a mission that will change history for the lucky few her father has selected.
Gemma's parents are adamant that secrecy is paramount to her family’s safety. If people knew what they were capable of, they could be "used and abused", as her mother always says. Afraid she might accidentally utter the truth and break the ancient oath of her people, Gemma spends her school days as a loner. Only one thing can throw her sheltered life askew... Harrison Granger.
Harrison never expected to talk to the strange Hart girl, but after a brief encounter he can't stop thinking about her. He begins a campaign to chisel away her icy veneer and is met with unexpected consequences. As he slowly wins this girl over, he enters a surreal world that has him fighting to keep his newfound love and his life.
The blurb tells you everything and nothing. Gemma's fmily go back in time to right wrongs, to save good people from untimely deaths etc. In order to do what they do the family trains rigorously and has a strict diet - no fizzy drinks and no junk food. It is a cold, spartan existence for Gemma and her older siblings. Gemma had previously told her best friend the family secret and the family had been forced to move across country. Consequently, she is terrfied of interacting with others in case she betrays her family again.
Cue typical teenage story - new boy Harrison intrigues Gemma and vice versa. They meet accidentally a couple of times then Harrison sees her disintegrate into a shower of gold dust as she travels back in time (she is drawn back by her family with only a few seconds' warning).
Together Harrison and Gemma find out more about her time-travelling abilities and the different factions of time travellers and their opposing agendas.
The book isn't perfect, there are a few homonymic errors (vile instead of vial and peaked instead of piqued type of thing)but otherwise this was an intriguing story, well-told with good characterisation and lots of action.
Perhaps I can best compare it to the Vampire Academy and Bloodlines series (although it is completely different). It is a PG-rated story about 17 year olds with strong school elements, which is far more about 'odd' elements (time travelling vs vampires) and has a romantic element.