I hate self-pitying characters like this.
Bystanders to bullying cases, who persuade themselves that they are also victims. (Which is not entirely wrong, but far from the same level of victimization as the actual target.)
The part that is the most telling is how she laments that she couldn't save Rei because she was afraid for her life. I'll grant her that much. They were in a dungeon that far surpassed their capabilities and were... ah wait, totally safe because they were not under attack at the time and were about to use teleport stones to go back. So, a bit of a stressful situation, but far from an actual crisis. They even had even stones to bring everybody back, but three members of the party deliberately chose to abandon Rei, after stabbing him. It wasn't a "necessary sacrifice" so much as a straight-up murder. Still, I'll grant her the "fear for her life". Not so much because of the dungeon monsters... but more because of the three human monsters she teamed up with.
The problem is what happened afterwards. She disagreed with the party's decision, she saw her "friend" be tortured and left for dead, and still she stuck with this party... who went on and "sacrificed" several more healers in the same way. At this stage, this is not a "fear for your life", it's outright complicity. So spare us the self-pity.
This chapter is supposed to make us feel sympathy for her, but I just can't. (Similar situation in
this manga.)
I'm not saying that it's not a credible characterization. Humans can and do behave like this. I just don't feel any sympathy for these types. There is a point where they lose it for me. For Feil here, that's after they killed another white mage. For that other example, that's when the "friend" allowed her party to go after the MC's party that last time. They might deserve redemption, eventually, but they have a lot to do to get my sympathy back. Wallowing in self-pity doesn't cut it.