I was just thinking the same thing. She's just a child. Besides, the system in their world is different from ours. We have child protection laws and slavery is a taboo. We have higher standards in our ethical values. The og fl is just trying to survive. I'm not saying what she did was ethical, but I can understand. I think it's just funny how many are so mad at the og fl when we have Dietrich who kills just as easily as breathing but they're okay with it.
Yeah, she's just desperate kid in a terrible situation who did something rash and unethical (though pretty smart in a lot of ways) to try and get out said situation. I'm sure a lot of other people would do it too who aren't even kids, at least kids have the defense that the judgement part of their brain isn't fully formed yet (and won't be for the most part until early-mid-20s give or take depending on different factors of course).
You have a point about Dietrich and how people react to him vs her, when one has done action FAR worse than than the other. Like he's been raising his little "sister" (or rather just a random baby to him, but one that grew up with him like a sister) and keeping her alive for the main purpose of getting close to her and sacrificing her (RIP to the MC bc not does the og ML want to sacrifice you, so does the og FL)(also, I know that he's starting to get second thoughts on that). Like don't get me wrong as I can make an argument for him as well, but that's not what we're talking about rn.
While what this saint girl makes me want to slap her, we have to remember this is a kid who was just threatened, tricked, and told that she's going to be made into a slave, so I feel like she just did the first thing that came to mind and thought quick on her feet.
The reason why I say this is, bc the last time she saw the MC, not only did she find out she was from this evil family (though she was confused af how the MC even from that family (*cough* it's bc she doesn't *cough*)), but she also saw how protective her brother was over her and the only time she ever seen the MC she was with a family member (she may or may not know the rules of which family members can come in and out of the estate just from her position of being the saint, as well for living there for awhile at this point)(I'm also not sure if she saw the MC's brother, but she may have out of the corner of her eye).
So, she probably put two and two together and went: "Well I'm in deep shit, aren't I? Oh wait, there's that pink haired girl from before from that evil family with her very protective brother, he's probably here too since kids can't come in her otherwise. If I get her involved or even this guy's full attention on her, then he'll leave me alone, and her brother will beat the hell out of him and neithee one of us has to get hurt! Hopefully since I'm the saint this won't backfire too much on me"
If this is the case, I'm moving her to Slytherin (Ravenclaw I feel like she shouldn't learned not to trust random guys after living in that area for even a year (though I think she's been there for a couple at this point, I can't remember tbh); there's probably way easier and safer ways to get to that Temple she wants to go to; and to not mess the MC and face her brother for having put in that dangerous situation to begin with like that (she was still being a bitch, a smart one, but still one in the end, considering the MC was getting up to help her anyways)).