Yup, i am smart af too, i am sure god would love me to kill the Hero, totally wouldn't please the Demon Lord at all, 500 IQ move.
The entire point of her fight isn't killing the hero, is keeping her occupied so all her "rebellious companions" are killed by the others, she can be subdued, and the sword that strengthens the levels of the [hero] class takes effect to make her a puppet of it.
My issue is more along the lines of what others have said, mainly:
1. How did she know that what the demon and Ares are doing is trying to make Ruti virtually unable to oppose her class?
2. How is she not trying to kill the demon first and then sucker punch Ruti to give her the sword, if she somehow already had an idea of their plan?
3. Not how she isn't trying to convince Ruti of her duty, because I'm pretty sure Ruti IS already conscious of it, but prefers to ignore it. So instead she's trying to justify the need for her actions mostly to herself,as to not falter in front of the opposition her comrades are showing