Ahh I seem to see how you reached that consensus as the conversation with Sword Maiden at the end can be rather ambiguous on its own but I think you may have misremembered certain scenes.

In the manga SM talks about issuing quests to adventurers to go and slay the goblins herself. But then she says that none of them ever came back.

Y

She later tells Goblin Slayer that was part of her plan, to ensure no adventurers that went to kill the goblins ever returned so that people would fear for their lives.

Please source this. She never said that her plan was to ensure no adventurer returned alive

She also talked about washing herself frequently to wash away the sensations of everything her familiar had done in the sewers. This strongly implies that the familiar, and therefore herself had a hand in the demise of the unfortunate adventurers. She even asks Goblin Slayer if he would kill someone that was aiding the forces of chaos when he first arrives. SM is wracked with guilt, she wanted to confess to her horrible crimes. That's why she came clean so fast. She further asks Goblin Slayer what he plans to do with her as she expected a heavy punishment for her crimes, but since she isn't a goblin GS didn't really care. She even knew about the mirror, and everything that was really going on yet she told NONE of it to GS and his party. Bottom line they were not supposed to survive. She intended them to be martyrs and to further increase the peoples' fear of the goblins so that they would be taken as a serious threat. You have to look at the subtext sometimes, not everything is plainly explained to you in exposition all the time.