It would probably help to tone them down. I have a client with very bad vitiligo and was worried that the tan would go orange on the non pigmented areas, so we just did a free patch test on an area to see how it went. It was great, didn't have a totally even coverage but it really toned down the difference between the two skin tones and she was so happy and has had two tans since then. So just patch test and see how it goes. She'll really thank you for it, it's up to you if you want to make a minimal charge.