Sarah, I'm so, so sorry for your loss! Please don't beat yourself up over it! I've been following your thread all day, I also have a first-time broody sitting on a few eggs on day 23 and I was starting to worry and wonder if I should intervene. No pipping, no cheeping that I can hear, but I think I'm just going to wait a while longer and hope for the best. I don't know if I'm doing the right thing, either. Thank you for sharing your experience. I'm so sorry it didn't turn out better.
As for your broody - it all depends on her. I've had some sit for 6+ weeks and others leave at 3 weeks. If you could find a newborn chick or 2 for her, that would be ideal. But if that isn't possible, I'd probably put another couple eggs under her, but give her some free eggs or something you're not emotionally invested in incase she leaves the nest.