I would try to match the lighter beige in granite, so a couple shades lighter than oat straw.

If she has an extra piece of the granite, she should bring it to the store when looking at pain colors. They may also be able to "match" paint to it. How? the device they use takes a read on all the colors in the sample and usually comes up with a good complementary color. This would mean a wall with little contrast. If she wants the feature wall to really take center stage, then contrast would be better. The Oat Straw would be a good candidate. Ben Moore also has several decorator whites that would give her a bit more flexibility if she likes to change things up with pillows, curtains, etc., throughout the seasons.

Maybe try matching the lighter shades of beige to give you color palette to work with!