If she wants to try it, I had that happen to a Parchment white leather tote I have. I used gentle baby wipes on mine and it came off. I'd try it in an inconspicuous spot first, just in case.
One method is using a white (pencil) eraser, and literally 'erasing' the color transfer. I've tried it on vachetta leather that had (denim) color-transfer on it, and it worked! But I have no idea how it works on other types of leather... If you try this, as CoachMaven suggested, do it in an inconspicuous spot first.