Well I don't know about a high-calorie formula, but I would honestly suggest that you take a step back and listen to the doctor and other hcps. I know exactly how you feel, really, and I'm not saying this to be critical. My dd was born 8lb 4oz, lost over 10% of her birth weight and took 5 weeks to get it back. She's also been quite a small eater, and at one point wouldn't touch anything but bread and cream cheese, fruit and yoghurt.
I won't say it didn't sometimes make me anxious - however, three things reassured me, and I hope you won't mind me sharing them with you in case any of them apply to your situation too.
Firstly, I'm small (5'3" and 8 stone) so initially I assumed that she was readjusting. She was born in the 75th centile, but as I'm probably in the bottom part of the 25th, and her father, I would guess, is in the 50th, I thought it likely she was just adjusting downwards to her natural size.
Secondly, I know for a fact that I used to eat tiny amounts of food as a child - I now eat like a horse and there's pretty much nothing I won't eat. My mother never used to force me to eat or fuss me about it. She just used to put healthy food in front of me and take it away again if I didn't want it. My tactic with my daughter is that if she doesn't want what I've made for her she can have bread, yoghurt or fruit, but I don't cook her another meal.
Also, it might be useful to look at what she eats over the course of a week rather than being worried if she doesn't eat much in any given day or two - if often evens out more than you think.
Thirdly, my daughter was about the same weight as yours at 14months. I figured that if she was healthy, energetic and sleeping well then that was a sign she was getting what she needed.
I really understand why you're worried, pariticularly since you had to go through the anxiety of reflux - it's really scary to think they aren't getting what they need. But really, you'd be surprised how little some babies and toddlers need.
And regular full fat cows milk has lots of calories, and will certainly, unless she's allergic, prevent any danger of her not thriving. Just keep giving her as much of that as she wants, and, honestly, she will be fine.