Okay, so... For those who want this GL tag to be real, I apologise, but there's no tag for it in the original WN. Normally, they'd have (girls love) elements, but there's only (violent depictions), which is to be expected of a story where yes, the point is she's rescuing villainesses, who would normally have come to bad ends without being given the chance to be high-spec, and making them her aides in a kingdom run by villainesses.
That is the plot.
As to why she got murdered? Well, a stab with little warning, or a carriage crash, or any number of variables could have happened... But instead, some random queen turned up and she had the room to do her thing, instead of getting ambushed. The novel doesn't really go into detail on this one, although it goes into some detail with further Avoided Bad Ends.