Help Required - Personal Trainer/Nutrition

I'm interested in replies to this so BUMP for later.

We have exactly the same stats and I'm currently at the weight you'd like, and dropping more.
Disclaimer: Not to say we are exactly the same metabolically speaking, this is just my story.

Getting my correct (DEXA scan, AKA, an x-ray of my body density) body fat percentage REALLY helped. I realized that half of my battle with weight was focused on starvation and lowering calories without paying attention to the amount of carbs, protein, and fats I was taking in. This is critical to weight loss and even disease prevention. You can lose 8 pounds and gain osteoporosis (my story), or lose 3 pounds and gain a metabolically active life even into your 60's and 70's.
I found out I have 23% body fat, which is athletic. I still wasn't happy with my body composition, so I knew fat burning was my only option at this point.

The main deal is, try things on for size.

Low carb? OK, give it a go. See what your body does. Are you utilizing resistance training? This was one step, extremely difficult, that ultimately gave me muscle structure and tone and fat loss. If you lower your daily intake of calories, you will begin to burn muscle for fuel (if you'd like more literature on that process I can point you in the right direction). Fat is stubborn, you gotta ease it out with long distance/duration cardio. You also have to build up your muscle stores so that it doesn't widdle away.
Personally, I had a lot of bloat and weight retention due to grain and fruit consumption so I keep them VERY minimal.

High carb? Calorie cycling? Raw vegan? Whatever diet YOU feel is best for you, give it a try. Exercise can only tone and shape what you've already got. Your fuel, your diet, is what gives way for your desired changes to the body composition.

The amount of calories varies from person to person-- eat what makes you feel satisfied and log it. See where you end up.

The three best tips I can give for the weight and body composition changes I experienced are:
1. Do NOT consume sugar, added sugar, refined, sugar. Fruit and starchy tubers, duh. But candy, cookies, lollipops, whatever is not a nutritious food that fuels your system to burning fat. If you really want sweet treats, ask me about my sugar free cookies and muffins.
2. Drink more water. Seriously. A cup every 1 1/2-2 hours. You know this is smart.
3. Always remember that exercise is for recreation and fun. Do what gets your heart pumping and makes you excited. If you look forward to it, then you're golden. You'll work out more, sweat harder, and become faster.

First, I am wondering why you feel the need to get down to 123? How did you come to concluding that that is how much you should weight? If I were you, I would try to get a reasonable estimate of my body fat and make my goals from there. Here's a calculator for that: http://www.cordianet.com/calculator.htm

At your weight, and from the description of how you lost weight, I'd worry more about building strength than losing weight. Hopefully, your trainer has incorporated challenging weight training routines into your regiment.

As for your trainer's nutrition recommendations, I have not idea why he thinks you should eat that much protein and that little carbs. If you are on a diet to lose weight, the general recommendation for protein intake for women to avoid muscle loss is 1.1-1.2 grams per lb of lean body mass (your total weight minus pounds of fat). You can generally eat less protein if you are maintaining. So I don't think you'd likely need to eat more than ~120 grams of protein. As for carbs, you'd need to eat above 100 grams if you want to avoid ketosis (I have no idea if you want to induce ketosis on your diet). If you're doing a good amount of cardio, I don't know if it's such a good idea to consume so few carbs.

Honestly, I'd recommend that you ask your trainer a lot of questions about the above issues. And where he comes up with the diet plan he formed for you. A lot of trainers really have no idea what they are talking about.

Here's where I got most of my info, if you want to learn more: http://www.bodyrecomposition.com/nutrition