My post isn't really to give ideas to help, more to say I understand what you're dealing with and to talk about my own situation and thoughts. I know, a bit selfish, but maybe someone can relate. I also think talking about things can sometimes, bring about important problem solving ideas for issues like this.
I have a 5 yr old who whines, moans and complains so much about every little thing, that I sometimes wonder if there is something wrong with her. Some of it sounds like the whining of a spoiled brat who always gets her way, but as you said about yours, she doesn't always get her way. We try to be very adamant that there will always be times that she won't or can't get what she wants. We try to push the ideas that we all have to help each other out, need time away from others, need time with others, need to treat everyone with courtesy while still sticking up for ourselves, need to be patient, need rest time, need to respect opinions of others, etc. We frequently withhold things she wants because she needs to learn to live without, or we just don't have time resources or energy, or are busy with other things. We try to be respectful of her also, letting her know our plans in advance, asking her opinion on things, discussing why or why not her ideas may or may not work in a given situation, and just plain talking with her (not just too her) about important and even unimportant issues. We remind her frequently that no one is perfect, we all make mistakes because we are all human (including mom and dad), and that doesn't mean mistakes make a person bad only that the choices made were not good.
Maybe a bit much for a 5 yr old to ingest, but she has a pretty large vocab and has a good grasp of abstract ideas. Still, she often whines if anything is slightly out of place, doesn't happen right now, isn't just how she wants it, isn't fun, doesn't go along with exactly how she thinks it should, isn't entertaining enough, and the list goes on. I know that little ones tend to be very egocentric and have trouble seeing things from another's point of view. Some of her frustration seems to come from that narrow viewpoint, but some of it seems to come from an almost perfectionist point. Like she thinks that everything has to be perfect (her view of perfect), or she gets totally bent out of shape (this also seems to be rubbing off on my 3 yr old boy). That just drives me crazy, because I can't stand that kind of unbending perfectionism, and I really can't stand the whining and negativity that stems from it. Though I try to do the best I can in most situations, that is the one thing that I don't seem to have any tolerance for. I react in the worst way, which I know isn't helping anyone, and is likely causing a great deal of her overreactions because she sees my overreactions.
I guess I went a little off into left field. These are just things I frequently find myself struggling with. I like to consider myself educated when it comes child behaviors, but these things really bug me, and I don't feel like I deal with them well at all. It's like I'm fighting over what I know in my mind is appropriate or inappropriate based on education, and what has been ingrained in me from past issues that are far different from that education. You know, the old ideas that children must respect their elders(no matter what), stay out of adult conversations, do what they're told, don't know enough to be included in adult conversation, must deal with whatever they don't like, must listen to adults talk to them rather than with them, etc. There just seem to be so many things that were common place when we were growing up, but are not considered appropriate by early childhood standards today.
Many of the things that have changed I never agreed with growing up anyway, yet I still struggle with not treating my children in the same way I hated being treated when I was young. Why is it so hard to stop these things when I never agreed with them in the first place? I guess judging from what I've written I feel like my child's attitude is because of my actions, yet I am mostly at a loss for what to do about that! I also acknowledge that some of her attitude has to be from her age and just the kind of person she is, but it still drives me bonkers. It would be nice if we both would just tone it all down a few notches. Part of me feels like I am the adult, and I should be able to adjust my own negative behaviors and tolerance thereby helping her adjust her own, yet part of me feels like she shouldn't be getting so bent out of shape so easily when she knows I don't like it and never react well towards it. I realize it has to be some kind of balance, but were to begin, and how to adjust my own negativity seems to be beyond me.
Buy the way I do tend to post very long posts like this. I am just always analyzing things and feel like I get better results if I go over everything in my head, and maybe get input from others as well.