I'm not sure it relies on OOC information that much?
X can see the three situations, but she also knows the girls, and can infer things from that.
Argalia can easily be justified IC as the unknown enemy maybe being as dangerous as Winchester just was, while not going for Sayaka can be simple trust that they can get out of this, and taking into account that if Kyoko can pull out her fire, she is very difficult to put down.
You can also say that X is prioritizing the fight that will take the less time, so that she can come to the rescue of the others quickly with more force on her side.