Hm. You say you don't really want to keep this hen. But how are you any better than them if you give her back to them, knowing what her fate will likely be? It may be awkward or uncomfortable talking turkey to them, but what have you got to lose? Are you really good friends with them anyway? Speaking for myself, (and I'm a crusty old broad now), here's how I think I would handle it. I would say to them, "Look, you don't have a very good track record with chickens. So if I give this sweet girl back to you, you have to agree to take good care of her. And that means, at a minimum.... you shut her up at dark and let her out in the morning. You (name what you think she needs). And if you're not willing to care for her in these ways, then I think she should stay here with me." What's the worst that could happen? They don't come over and play Scrabble with you any more? They probably already don't.
Think about it. And do right by this chicken. But like I said, this is what I'd do. But you're not me. Best wishes.