I legitimately could just let her die for the reasons you say. Especially since I was doing a neutral evil playthrough at the time. I guess my Lolth-sworn drow felt really frustrated at having to strike deals with a heretic like Minthara, so the second she was out of the room, I looked for an opportunity to undermine her authority behind her back.
It's just I dunno from a roleplaying standpoint, when your evil character only does evil things 100% of the time, the story gets really boring. To counterbalance that, I look for opportunities to do a minor good deed once in a while, so my character doesn't come out as a one-dimensional prick. So yeah maybe this evil drow warlock did end up massacring a whole grove-full of innocent refugees to win points with an evil cult she plans to betray later, but on the other hand somewhere there's a little goblin who didn't die thanks to her. I like that.
My Lolth-sworn drow let the bitch die, struck a deal with the Absolute-sworn drow, then betrayed her when she ended up attacking the Grove. Posted about that in the Feedback section.
