Is this Rush (2013) by Eve Silver...? It's the first book in the The Game trilogy.
According to the blurb on the author's website, the protagonist, Miki Jones, is a sixteen-year-old girl who's mysteriously healed after being run down in the street, then pulled into a game of some sort and sent on missions with other teenagers to eliminate alien creatures known as the Drau.
Sixteen-year-old Miki Jones’s carefully controlled life spirals into chaos after she’s run down in the street, left broken and bloody. She wakes up fully healed in a place called the lobby—pulled from her life, pulled through time and space into some kind of game in which she and a team of other teens are sent on missions to eliminate the Drau, terrifying and beautiful alien creatures.
There are no practice runs, no training, and no way out. Miki has only the guidance of secretive but maddeningly attractive team leader Jackson Tate, who says that the game is more than that, and that what Miki and her new teammates do now determines their survival and the survival of every other person on this planet. She laughs. He doesn’t. And then the game takes a deadly and terrifying turn.
According to this Goodreads user review, Miki has eight years of kendo training.
Miki Jones stands out in more ways than one. She lost her mother when she was fourteen and she and her father struggle with their grief in very different ways. While her father drinks himself to sleep every night, Miki desperately wants to control every aspect of her life. She is no shrinking violet, though. When she gets pulled into the game, she takes some time to adjust, but once she does, no Drau is safe from her. Eight years of kendo guarantee her physical readiness, but her bravery and adaptiveness come from a different place altogether. Even more importantly, Miki’s steel spine doesn’t mean she’s emotionless; she experiences pain and loss and grief just like everyone else, but she never wallows in self-pity. Moments of insecurity come and go, but each of them leaves Miki stronger and readier to face life, both in the game and outside of it.
