J....my son had severe failure-to-thrive for the first 3 years of his life. I was constantly trying to figure out ways to "superfat" his diet to get not only protein but fat into his diet.
We worked with a nutritionist and feeding nurse through Early Intervention from 18 mos. to 2 years. We're in York County...I'm not sure if all counties have these services through Early Intevention, but it's definitely worth a phone call! They came into my home, watched what he would and wouldn't eat (and how he would & wouldn't eat those things) and then gave me a personalized plan and goals. The most helpful to me was the calorie goals the nutritionist gave me - he needed X # of calories to maintain his weight and X # more calories per day to increase his weight.
For now, here are a few tips (my son gags when we cook meat - the thought of putting it anywhere near his mouth is a joke). If she will eat eggs, add a tablespoon of HEAVY CREAM to them before you cook them. Heavy cream is the easiest way to add fat (that directly translates to calories) as a little bit has a ton of calories and goes a long way.
Another good one is cheese, fat and calories in one - not of the American variety...cheddar, etc. When Riley would eat eggs (he won't anymore) I put cheese and heavy cream and voila...
Yogurt is a primary food in Riley's world...even now. The YoBaby is made with whole milk. There are very few yogurts that aren't "lite" - you don't want anything light or low cal. Smoothies are another one - fruit, yogurt, whole milk and a little ice.
The docs have probably told you to avoid peanut butter and other nuts because of her age - because Riley's weight was so low and we have no family history of any food allergies (that's a big one) they said, if he'll eat it...feed it to him. Of course he wouldn't - the stickiness of the peanut butter caused an immediate gag response. I still try this one now and then, but without success.
I have also had good luck with breads...pumpkin bread, banana bread, even zucchini bread. They take no time to whip up and they are tasty.
Unfortunately, everything I can suggest is dairy-based because that was the only way we could increase calories with protein. When it came to the "booster" calories...I would do things like fruit snacks (80 calories a pack) and goldfish crackers. They didn't add protein, but from every feeding therapist, nutritionist, doctor and feeding psychologist we worked with (and there were many) it was always calories, calories, calories. When I mentioned to one peds GI specialist that Riley's new food was McD's french fries...her response was, "then have him eat french fries every day...we'll worry about his arteries when he's 50."
Finally, I believe it is Kirkwood Labs that makes a protein powder from golden peas - it is odorless, tasteless, etc...you add a sprinkle to everything you possibly can and it packs in the protein. You can add it to baked goods (cookies, breads, soups, whatever) or as is to whatever she will eat. There is a calorie booster called Benecalories that we were told to use by the feeding clinic at the University of Maryland - it was NASTY and he busted me every time I tried to put it in his food.
I hope this helps. There is a great book called, "Just Take a Bite" that has a lot of strategies for getting food into kids who don't want to eat.
Good luck...as a mom I don't think anything made me feel more helpless than not being able to get my child to eat. Now he is five and is on those precious charts - barely, but better than nothing. He eats about 5 things, but he grows steadily and is pretty healthy overall. We take what we can get - but it was a long road.