I think the amazing thing wasn't that she was angry specifically at the contamination of the crime scene charge. She wrote that she was furious at the idea that she and Gerry could do ANYTHING that would put their child in danger.
As far as the food or drink goes, I just know if I needed something to drink like coffee or a soda or water, I guess I'd just ask. I wouldn't expect them to offer it to me, I'd ask if there was somewhere I could get some, or I'd call someone to bring me something, etc. It just seemed like an expectation of a certain kind of treatment that was not realistic or appropriate under the circumstances.
Also, if you look at the writing closely, there's nothing there that is in any sense revealing or personal. There just isn't anything that comes across as natural or not scripted. So one of two possibilities exists:
1) Kate is a very controlled, self-disciplined person, to the extent that writing this was like writing a doctor's report for her. Very factual, she makes an effort to write about Madeleine in an emotional way, but that's the only real hint of emotion. So it could be that Kate is just naturally this way, but that argues also for being self-controlled and self-disciplined enough to pull off hiding an accidental death.
2) Kate is writing all along only intending this as something to be published and released--a very self-conscious kind of memoir. It's not a real diary or journal for her feelings or releasing stress, it's meant from the beginning as something to be publicly released. A rather calculating publicity act, in that sense, but no different than other acts from the McCanns.