The nutritionist is your adviser, not your boss. She is free to recommend whatever she thinks is right, but you are free to decide what advice to follow and what to disregard. The way to deal with any expert, whether your doctor, your CDE, an author, or your next door neighbor, is to take what you can use and leave the rest.
She does not live in your body and she can't ever know it as well as you do. She hasn't been there with you through the years to observe what works and what doesn't. She isn't there 24x7 managing it, you are. And -- bottom line -- she gets to go home at night. Meaning, she doesn't have to live with the consequences -- YOU do.
In case I haven't made my position absolutely obvious, you have not only the right but the responsibility to yourself to make the choices that work -- that produce the outcome you want. Nothing trumps that. Period. Full stop.
You might also get some reinforcement -- or at least a chuckle or two -- from this discussion. :)