Or… He killed her already after the bath scene. After he told her about te faith of the wessex village. He didnt just cut her hair but her head. Maybe that was Yidus head he talked to in his tent. I belive so.

Ragnar takes Yidu to his secret hut, where live exotic snakes crawl around in the middle of winter. She turns out to be exactly who he imagines her to be. She is not real to anyone but Ragnar. Noone even ever looks at her.

Yes, Aslaug bougth her in the harbour and ones when Yidu tells her that Ivar is crying for her. Aslaug never speaks a word to her though.

I do not think Yidu was even a real person but a product of Ragnars drug infused mind and a personalisation of the drug itself. Auslaug bougth drugs and gave them to her husband in an attempt to slowly kill him. Yidu didnt ever talk to anyone else and noone talked about her exept from Auslaug.