How about telling her without having her jumping through hoops to 'prove herself' as you put it? Letting her do so to make sure she doesn't need to sounds too Kunning to me.
It is Kunning because if she screws up a plan she made entirely on her own, she'll hopefully realize she's doing something wrong and will be less eager to "prove herself" further. Also, anime logic, which the CYOA seems to apply sometimes.
Lastly, 2-A sounds like Erd will demand her to stay with us by taking advantage of her oath, which is something she can take wrong and if she does she will be less willing to talk with us for a while, worsening the issue.
And also, I don't particularly trust her, thank you for asking. It's not about betraying us, though it is up in the air if those voices wouldn't make her an offer she can't refuse (what happens if they offer her solution to her problem?)
I had the same thought and honestly, yes, it is a risk, but so far we know there are only two ways of "acquiring her father's legacy": 1. Marriage and insemination (which won't work for now, even if she really wanted to
) ; 2. Forceful heart/soul extraction, a process which will no doubt prove lethal for Erd. I'm confident she no longer hates him that much to the point she would do the latter without hesitation (she even mentioned Erd would make a good demon, which I suppose it could be considered a compliment). She might be lied to, but that's again part of the risk.
First, it's not her problem, she just wants to make it hers and deal with it on her own. That's exactly the kind of attitude I am trying to rid her of.
Second, how much confidence does 'I crossed blades with them twice and got owned/tricked both times, do not worry, I'll be fine!' inspire?
Well, the first one can be dealt with by sending her. If she fails, that will certainly temper her attitude. If she does it successfully, it won't be without great hardship and without missing the commodities of having an entire army of servants to do her chores and other people to give her company.
The second one... No idea, it would help if we knew what kind of spells and techniques she has available, but sadly we don't have full access to her sheet.
Perhaps she's aware of the "third time is the charm" rule?
In fact, considering she can teleport back at any time (twice if she knows how to draw a circle), there's nothing stopping her of literally dropping by whenever she feels lonely/has something important to discuss with us.
Simply put, I think we would be able to get more out of her if we watch each others' backs - and if we can fix her messed up head at least a little in the meantime, that would be the greatest reward I could ask for.
Unfortunately you know that won't happen until she grows up from her childish phase, which won't happen anytime soon. If only we knew what's her current relationship meter and which option would raise it further...
Also, we don't know if there will be time to talk after the adventurer's expedition. The aftermath will be world-changing, no matter how much we try to downplay it.
EDIT:
That aside, I don't think we do know how to do it with cat goblins unless Trider had a much wider ranging scope of lovers than I'd anticipated, so I'm not sure how much advice we can give to Arlin. Hey,
treave, we're not playing as a furry here, right? Right?
Considering he was desperate enough to betray his race and his (former) friends for the off-chance of getting some pussy, I would say he has not many standards about what kind of women he likes.
Doubly so considering he started doing this since the Academy, that is, when he was about 12/13 tops.
Oh, and one of his first uses for the unique spell he created (if not the primary goal) was to spy on women.