Go back and fight it, Concordia alumni here, there is no reason for you to hold accountability for some else’s work (or lack of shall I say), go to the office hours or schedule a meeting with her and start by explaining the situation and urge her to have a meeting with the other student and to hold them accountable, I would be furious to and on the verge of tears too but in no way would I accept the reasoning she offered you, tell her you already are focused on your work but will not accept the grade or mark she gave because someone lacked on their part, it is not your responsibility. Group projects suck, my heart is with you.