As for the future, -1 to attempting to recruit Proxxy. My reasons for this:
- It probably won't work. The only reason we were able to recruit Riltia at the beginning was due to her having no clue that she is a Sibling and therefore should be working for Oric and trying to kill Ciro. It's possible she still has no clue.
- Proxxy is powerful. If we want to have a snowball's chance of killing her, we will need to strike quickly. We need to get an attack in first. Attempting diplomacy will just open up ourselves to an attack.
- We are supposed to kill Proxxy. If we want to advance in the story, we'll need to do what we're meant to do: kill Siblings. Proxxy is hostile towards us, and will try to kill us. We need to kill her first. In the words of Captain Malcolm Reynolds, "If someone tries to kill you, you kill them right back."
As an implication of #3, like I stated earlier, we will need to kill Riltia at some point, too. Not yet, because she's useful and friendly. But if she stops being either one of those, we should consider actually doing what the angel statues told us.
1. Our shotgun diplomacy is strong. Proxxy would probably rather work with us than die, at an absolute minimum. More likely, she has plans of her own and therefore some measure of use for us.
2. She has 8 hp, and her strength is another reason to recruit her. If we can't afford a round of diplomacy, we shouldn't have engaged her in the first place, because we're probably a bad roll from her murdering us even if we do go all in.
3. We have no reason to believe this other than that it's been implied to happen in the past. It wouldn't surprise me if we need to
defeat Siblings to get deeper into the dungeon, but we're not even a hundred percent sure of that. You're also mixing this argument with "she's hostile therefore we have no choice," which implies to me that you know neither argument is really valid.
Also, I'm offended at the notion that we should kill one of our only friends and possible romantic interests because a statue told us to.