Mirea is kinda right tbh. The elf is one thing, but Naga is definitely beating them up and capturing them once she gets her mana back and has a way home. I wouldn't put it past her to kill them (I mean, that wouldn't actually happen because this isn't that dark a story, but Mirea and Naga don't know that). The elf I think is not as tough as she sees herself. I think she would have a hard time hurting soneone she knows personally.
If I were them I'd incapacitate the big dude (maybe with the paralysis slime?) and then focus on assassinating the dragon and then the elf. Apologize for getting the human involved and then dip.
I wonder if Mirea will get a boner while wiping down Naga.