I have a feeling we won't be seeing the last of the beautiful Karina aka Mini Anden. My personal speculation (not based on any spoilers) (and what seems to be the consensus) is that Karina is 'Sarah's' little sister. She's ultra competitive with Sarah, which can be explained by sibling rivalry and her main goal is taking what Sarah wants, even when Sarah doesn't know she wants it.
Most likely they're very close in age, hence the hyped up competitiveness, plus I have no doubt that Sarah probably always excelled at what she did, while Karina was the troublemaker in the family. What balanced Karina out for me and makes me want to see more of her is that she was expressing genuine sympathy to Sarah over the loss of Bryce and when the chips were down, she did come through for Sarah. I also liked the added touch of Karina saving Sarah's fish.