I Was, Am, Will Be Alice

Winner of the 2015 A Woman's Write Competition for fiction!
When Alice Carroll is in grade three she narrowly escapes losing her life in a school shooting. All she remembers is the woman comforting her in the moments before the gunshot, and that one second she was there, the next she wasn't.
It's bad enough coming to terms with surviving while others, including her favourite teacher, didn't, let alone dealing with the fact that she might wink out of existence at any time.
Alice spends the next few years seeing specialists about her Post Traumatic Stress as a result of VD--Voldemort Day--but it's not until she has a nightmare about The Day That Shall Not Be Mentioned, disappears from her bed, is found by police, and taken home to meet her four-year-old self that she realizes she's been time travelling.
Alice is unsure if her getting unstuck in time should be considered an ability or a liability, until she disappears right in front of her high school at dismissal time, the busiest time of day. Worried that someone may find out about her problem before long, Alice enlists her best friend (and maybe boyfriend), Pete, to help her try to control her shifting through time with limited success. She's just about ready to give up when the shooter is caught. Alice resolves to take control of her time travelling in order to go back to That Day, stop the shooting, and figure out the identity of the stranger who'd shielded Alice's body with her own.