Christina is a seamstress that works at Mode and also Betty's friend and confidant.  She is originally from Scotland where she married a man named Stuart who shows up in seaosn 2.  Christina is also the surrogate for Wilhelmina and Bradford's child.

Christina McKinney Quotes

I had a piece of your hair tested. They found Oxycontin and heroine. It's like Rush Limbaugh and Amy Winehouse fornicated and had you.

Christina

Betty: But I'm working for Wilhemnia.
Christina: I know, The wicked witch of the east side.