The fundamental structure of the human consciousness was such that the human could truly ever focus on only one thing at a time. Even if one felt that they were thinking about multiple things at once, this was not true. It was an illusion, what was actually happening was that the mind was thinking about multiple things in extremely rapid succession, making it seem like it was focusing on multiple things simultaneously.
This was the same mechanism that processors worked through, they could only engage in one distinct process at once and switched between many in extremely rapid succession.
It was because of this that in the brief moments where she had to focus on Kane, Rui's attack had almost completely landed on her!
As an experienced Martial Artist, she quickly realized the exact mechanics by which Rui was able to land powerful attacks on her bypassing her active defense due to effectively exploiting a momentary mental blindspot.
Yet she underestimated what was happening.
