While playing as a human with the missing sister background, when Logan asked me what my sister’s race was, I selected Krytan, and she appeared as a Krytan, with dark skin and black hair, during the personal story mission in question.
However, in the end game, after selecting the vigil’s plan to attack Orr, Deborah appeared as an Ascalonian, with white skin and blond hair, during the Marching Orders and Armor Guard missions, she did however appear correctly as a Krytan during the “The steel tide” mission.
In all instances however she did have correct dialog where she recognized me as her brother.
The other instances of Deborah should probably check what you race you selected for her, if you took the missing sister background, so her appearance remains consistent.
Also, according to the wiki, her appearance is randomized in those Orr mission regardless, you should select one specific version of her to use in all those missions, ans its very odd she magically cahgnes races all the time.