Get a colour match done in boots, they do different ones, no7, Esther Lauder, max factor. Once you know the shade then you can buy what she needs, in terms of contour, you want something 1-2 levels darker than the foundation, I always go for 1 shade darker as you can build.
If you don't fancy going to boots to get the colour match, use the testers in shops by matching to the jaw line, don't try to match to her hand as naturally your face tends to be slightly darker and has different pigments than the hands due to weather. Get her a good moisturising primer from under her foundation and makesure she knows how to properly remove it, plenty good cleansing products on the market these days, try to avoid things that contain alcohol as it dehydrates the skin xx