There are products called whitening skincare that are made for this. You also need to wear sunscreen while doing this so as to prevent more sun spots. However, she has to know it's not something that fades in a clasp of fingers, it takes a few months at least. I suggest she checks online shops for asian skincare, they have a lot of skincare ranges to choose from (although most use the same base ingredient called arbutin), complete with cleansers, serums, moisturizers, masks and sunscreen. Shiseido has some whitening products for example. I would suggest she'd be careful if she has a sensitive skin as whitening skincare can be strong.