I don't think you have a daughter in this game, I think the girl you are referring to is your sister, the girl you meet at your house. But I agree that the only choice is saving one them sucks big time, there could have been some requirements like raising your strength level to a certain point to actually stand a chance against them or something like that. I hope that the dev plans to add something in the future to save her.
Oh and NTR means two things, Netori and Netorare. Netori is when you, the MC, steal and fuck other people's girls. Netorare is when other people steal your girl(s) from you and fuck them. You'll find tons more Netorare games than Netori games tho, and they usually involve fugly guys/old men.