A lot of kids don't like their high chairs at this age - but you could certainly try a booster. What about the type of formula meant for toddlers - I think it has more nutrients than just cow's milk. And you CAN'T force her to eat - you're right! All you can do is keep trying. I'd keep offering new things too - with my dd, what she hated one week, she'd love the next. Focus on high calorie foods if you can - avocado, eggs, cheese, if she likes that sort of stuff. PB can be quite nutritious, I think! Try dipping sauces too - kids sometimes like that. If she likes pasta, you can often hide small amounts of veggies or protein in that. Does she eat better with other kids around? (Mine did!) If so, can you arrange play dates around meal times? What about finger foods while she's playing - snacking during the day can work well. I used to cut up avocado and as dd played with her toys, I'd walk over and pop a piece in her mouth until she refused. Same with banana, cheese, slices of egg, tofu (some kids love the texture). I also found at supper that dd was more likely to try something off of my or dh's plate - she wanted to eat what we were.
Try not to stress too much - a lot of kids get fussy at different times, and most outgrow it. If she's otherwise healthy - SOMEONE has to be in the lower percentiles, remember, or they wouldn't exist!
