Timehole - John Nielsen Book

Stacy Carver, a seventeen year old schoolgirl, embarks on a fantastic adventure through time and space. After sending an unmanned spacecraft off course, she inadvertently provides herself with the ability to create wormholes using a common garage door opener. To prevent this power falling into the wrong hands, she must battle evil, both past and present. Her journey finds her trapped in the Middle Ages, where she must fight for her life while seeking a way home to rescue her family from the dark corporation known as Shadotek.