Can you widen the lower jaw with braces in a 15 year old female?

Unfortunately, braces alone can not widen a jaw.  Braces can however widen the arch form of your teeth, but only up to a safe and acceptable limit.  A good system to consider for expansion and dental arch development is the Damon Smile system.  Keep in mind that if you truly have a narrow jaw, meaning there is a skeletal problem, you will need to consult with an orthodontist and oral surgeon for best treatment options.  Best of Luck! 

You can widen the dental arch (upright the teeth)  but not the underlying bone structure for the lower arch.Excessive widening of the dental arch leads to an unstable unhealthy result.  Some widening is OK but be careful how much is attempted!