We could always look at the bigger picture. We have, what, 9 teams? There is room for 2 more. We may never find out who she's racing with untill the cast reveal, but it's still worth it to look into her more.
ETA: I was looking back at the pictures and I found something that may help. Kiwi may be right, the ginger-haied girl could be with the a blue shirt guy.
On the subway with Terrance / Sarah, we already pointed out the yellow cap from the final 3 couple and the blue wristband on the other guy, but there may be something that was overlooked.
Purple: Terrance / Sarah
Blue: Blue Shirt Guy / Blonde
Yellow: Final 3 Couple seen in Moscow
Black: Blue Wristband
As you can see, the blue shirt guy and his blonde partner are on this train, yet he isn't wearing the same blue wristband as the blue shirt guy he is thought to be. That wristband is on a hand belonging to someone else, on the opposite side of the train!