Just don’t do it. No matter how she pleads or looks at you with those big blue eyes, or says it’s just for fun, that she just wants to try it.
Katie and I went to lunch at Nordstrom’s one Saturday, and afterwards, we went down to their cosmetic department to just look around. On a display case was a new product for “hair mascara.” It came in three bright colors – purple, pink and red.
Katie never ever asked me for anything (nor for that matter does my other niece or nephews), and for some reason (maybe it was because she was a Freshman in high school and wanted to see how she would look as a rocker chick!) the hair mascara captured her attention and she wanted to try it. “Just for fun,” she said, “I can always wash it out.”

If you ever face the dilemma of your niece wanting to highlight her hair in a bright color, I'd suggest you buy a removable purple hair extension instead!
Something sort of told me that this wasn’t something I should do – I was concerned that the dye in the mascara could ruin her long, pretty blonde hair. But the cosmetic clerk said it would easily wash out. So we bought it. Well it didn’t wash out easily. According to her Mom, it took about 3 weeks for the purple streaks to completely disappear. I’m thinking she was a little annoyed with me, but would never have said anything.