Sarah Grace is one of the Misc. Women characters that can be selected in the Outfitter. Her character model is unlocked upon reaching Multiplayer Level 50, meaning she is the last character in Women category to be unlocked.
She appears to be a French prostitute due to her accent.
At the very start of Exodus in America, Jake is being 'entertained' by a prostitute at the ArmadilloSaloon. This prostitute has the same hair and clothes as Grace, except her bodice is blue instead of pink, and her hair is black instead of brunette.