That Margaret is the textbook definition of "unable to move on".
Yes, her sister's died. It's tragic, and I'm not saying she should forget about her. But when your career choice is "fighting giant monsters and exploring dangerous locations", you should be more accepting that death is a very probable outcome! Having a grudge on the sole survivor is to be expected, but to immediately assume it was betrayal? Girl needs a good therapist.
That guy from the Fang guild is still the biggest loser. Can't be an adventurer without your ultra-reinforced gear? Sounds like a skill issue to me, buddy.