I have dark blonde hair, in summer it gets lighter blonde and of course, in winter, when im not in the sun, my hair gets darker. Well in 9th grade, when i was 14, i begged my mom to let me dye it blonder. Well she fought me about it until she had to give in. I WISH I HADNT, my hair got FRIED!! It was the most horrible experience and i wish to god i never dyed it ever. Ive been trying, since then to let my natural hair grow back (im 20 now) and ive finally found a dark blonde color that i hope will let my natural color grow back. I think a few purple streaks wont hurt at all, as long as theres no bleach involved, just make sure you use a semi-permanent, or ever a wash out color just so she gets the effect she wants for just a day and see if she actually likes it first!