You need to read up on Luo customs. There are quite a few articles on the net and a Luo musuem with pictures. It may have been quite possible she was a bride at 12. They could have sex with little girls but just not penetrate them. One girl could have multiple guys coming to her hut.They couldn’t penetrate until she was a bride..or some such thing.I just skimmed over it and don’t really remember what I read.
Customs certainly vary around the world, don't they? Even if she were a bride at 12, it seems to me that she'd be an unlikely attendant at a birth at that age. I'm speculating of course and assuming that a sister-wife attending a birth should be there to render assistance and support, and I have a hard time seeing that a 12 year old would have a lot to offer. It was a different world and a different time, and I'm glad it wasn't my family.