2009 Sentra and driving down steep hills at high speeds
 

I recently got a 2009 Sentra for my daughter and it only has Low for a gear. We live in Colorado so I would like to be able to use the lower gears when going down hills but when you shift it to L it seems like anything over 40 MPH is going to redline. Is there another option that I am not aware of for using the engine to slow down on steep hills in the mountains? I'd hate to have her burning up her breaks.