I had no problem with her being sexually adventurous or using her body as a way to bring herself comfort. It's not unrealistic- it's not a side of life or war that some people understand or can relate to, but it's not unrealistic. I also had no problem with the philosophical viewpoint of the male character, even if he was a bit unsympathetic as a whole. I liked that Rosenberg explained historical information without info dumps.
Also, I understand that sometimes there is an absence of emotion. For example, when her father writes her to tell her they have been ordered to pack bags and head east, obviously to be exterminated. At first it seems odd that Rita does not show emotion, however, upon further thought I wonder if it is one of two things: a) it is simply being left out because the nature of the story is already drawing emotion plenty from the reader, or b) Rita is numb. She has shut herself down emotionally to handle what is happening. I cannot imagine that losing people while worrying for your own safety lends much time or ability to continuously grieve appropriately. Since I have never been in the midst of war or a genocide, I cannot speak for how one would react. However, I will say, that this is part of the reason she is unsympathetic as a character. I'll explain further below in point 2.
My issues with the book came from the following:
1) The organization was haphazard. There was not any consistency and it was jarring to me. This was the biggest reason for my abandoning this story.
2) The pace was so slow. Snails move faster. This is not to say there wasn't any action - there was - it just felt like I'd been reading far longer than I actually had been. I think the fact the main character is standoffish from the reader is part of the problem. There is emotion felt from the events as a whole, but Rita is closed off not only from the war, but from the reader. She is standoffish and keeps the reader at a distance, which made me feel like I wasn't in the story. It takes a skilled writer to create a character who has so many complex characteristics and I think Rosenberg was more ambitious perhaps than he could pull off. Not to mention the male character (at least from what I read) was unsympathetic and I lost interest during his chapters (which, again, were thrown in every once in a while for one or two or three chapters at a time). I cared more about finding out historical tidbits than I did what was happening to the Rita or any of the other characters.
Now, this is not to say you would not enjoy this book. These are just my personal issues with it. I love WWII stories, but, unfortunately, this book was not for me. I liked it a lot at first, you may remember, but the more I read, the less I liked it until I decided maybe I was better off not reading further at all.