Maybe she should have checked the thrust levers were closed, but better not to comment too early. They may have been jerked open by a fall, manual dropping whatever. Maybe it was a dreadful mistake in starting with thrust lever wide open, but you must learn we all make mistakes in our jobs at sometime. A whole industry is built around trapping those errors so they become harmless. This was an unusual procedure, starting up in a hangar. Mistakes are part of life, that is why there are rubbers on the end of pencils (OK then, erasers to you Americans!). One hopes the young mechanic is treated with sympathy- can you imagine how she feels?
Now you made a serious grammatical error in your post. Work on that and trap that error before back to school time!
With many jets, the engine must spool up to idle before thrust position is recognised. From idle to full power for a CRJ- a few seconds. Brakes probably off as in hangar- movement very rapidly. By the time realisation happened, it would probably be too late to stop immediately.