If it is totally turned off it cannot be tracked, period. Not even the police would be able to track it.
If it is not off, then there are still two ways your mom could track it:
1. She might have installed an app on the phone allowing her to do it, for instance Find my Friends or Google Latitude. If you uninstall that app or change its settings, that would stop the tracking.
2. She might be tracking it through Find my iPhone.To stop that tracking, go to Settings, iCloud, and turn off Find my iPhone.
… but even if you prevent both of the above methods, although your mom wouldn't be able to track it, your phone company and the police still could do it if they believed a crime was involved or a life was in danger.