Being a fussy eater I thought I'd chip in.
When I was a kid I would never eat vegetables and the only fruit I ate was grapes and apples. Meat wise i didn't like anything but sausages, ham and chicken. And for the dread fish, never touched it.
I still to this day hate dried fruit and a lot of vegetables. I can't eat fish because the smell just turns my stomach. Meat on the other hand I love!
My mum would do the exact same thing as you've tried. She always attempted to blend things in or hide it in the mash. I could taste the difference, I still can.
I happily lived on carbs such as rice, pasta and potatoes with baked beans with a little bit of ham.
As a kid we weren't allowed fizzy drinks, sweets, chocolate, cakes or crisps. To this day I'd rather have flat coke than fizzy or just water. I have the biggest chocolate addiction ever but know how to control it and cakes I enjoy but not so bothered on. Sweets and crisps are not all there cracked up to be!
I, from a young age helped or watched my parents/grandparents cook, so would often make my own tea as my mum refused to make two meals.
My mum just left it be. I can't help my taste buds and if I don't like the smell of look of something I'm not going to eat it. I often went hungry as a kid, it did me no harm.
I know live with my partner so buy and cook all the food. And for the first time in all my 21 years, I ate mushrooms. I still hate them but I know I need to experiment and try foods. The only way I eat them is if they are blended to mush, then I can't pick it out and because I can't see it, I'm not bothered by it.
You can't force a child to eat no matter how old they are. All you can do is encourage and support. Put the option to try things on her plate and in her own time she will try it.
I was never given any extra supplements and my diet was shocking.
Still can't beat pasta, baked beans and ham! Nom nom!