Dark skin on feet?

I have a teen who is very embarred because she has darker skin on the top of her toes. She is fair in complexion and she simply wants a product to help her. I bought her a cream that is skin bleaching but it actually made the area darker. And I'm not sure why. Of course, she's not listening to her mamma about how beautiful she is and to not worry about it. Any suggestions would be appreciated. Thank you!