It doesn't matter if you are the world's most renowned trainer-dietician...she will probably never completely surrender herself to your advice on diet, traininng, etc. Actually, this goes for pretty much everything. Why? Because you are her husband. She will never percieve you the way others percieve you, regardless of your competence in this area. A wife is naturally resistant--immune even--to yeilding to the wisdom of her husband and letting him take control. This is not to say that things can't improve, but by your very position, in her eyes you are incapable of attaining expert status in any area that she struggles with. Sure, she will whine to you...complain to you...bitch to you...and even come off like she expects you to fix her problems, but she will never surrender and let you take the reigns.
Don't worry--it's like this with all women to varying degrees. They're inherently resistant to submission and refuse to admit defeat. Every marriage has its problems, right? All couples argue, right? Knowing that, let's look at the following example. Picture a typical wife and husband that get into an argument, but this husband just so happens to be a world-famous marriage counselor with multiple books authored on the subject. Do you think his wife is EVER going to sit down in the middle of an argument and be willingly counseled by her husband on how to deal with their conflict, even if he is providing the best advice possible? Hell no. He will get about as much respect on that subject as your wife gives you when it comes to training and diet.
Now, have this same wife sit down with a "different" marriage counselor, one that she doesn't know...even one with inferior credentials, and she will eagerly soak up everything he has to say. In the same way, you could allow your wife to hire some two-bit hack trainer who doesn't know jack-shit about training or diet and she will listen to every word he says...or at least try.
Over the years I have been paid by numerous people for my advice on the subject of BB'ing...most of whom never question my advice, yet my wife has just recently--in the last few months--began opening up to the possibility that I might not be a complete dolt when it comes to knowing how to lose fat and build muscle. For years she would second-guess literally everything I told her and ultimately end up doing her own thing. It didn't matter how respected I might have been by anyone else--to her I was "just her husband".
So, don't take it personally. When she whines, just listen to what she has to say and then tell her she is the most beautiful woman in the world and that there is nothing about her body you would ever want to change. Do this every time...and no matter what she says, never deny it. She will know you are full of shit, but she will be happy to hear it. Much of the time, women just want their husbands to listen to them talk about how they feel--not to fix their problems, so avoid offering up solutions and just listen emphatically. She will talk until she feels better and then it will be over--until the next time.