My mom won't let me get highlights..?

Im 14 years old and i have dirty blonde hair, I used to have light blonde hair but for some reason it just got darker. :/ I REALLY want it lighter again! And i went to a salon and they said highlights is the best thing i can do, But my mom says she wont let me, im too young, i have to keep doing it, it damages my hair , blah blah, But im soooooo bored with my hair color, D: Ive tried john frieda shampoo and conditioner and it didn't make as much of a difference and i tried the lemon method, didn't really work... So i really want highlights before the summers over D: How can i convince her!?! Or is there like some color mousse i can use? Oh and if i get highlights, How long do they last before fading,?Thnx (: