Let her off the hook? What? She just lost her son ( sort of like Gloria Vanderbilt, I might add) and was reeling from her own personal tragedy. I doubt that she was paying attention to any world news and besides, how well known was the situation in Germany, as it was happening, here in America?
Further, this woman was a total stranger--Kitty wasn't even sure of her place in Ogden's life. And, almost as she is leaving the Island she asks that her child be left behind. Kitty must have wondered what she could possibly be thinking leaving her child with strangers.
I would have had a lot of questions--no way I would have said yes without knowing the why? the how long? the what are we expected to do with him? The whole set up was strange,
Once things became clear and it was beyond Kitty's ability to help, she felt remorse. She should not have felt guilt