If chicken fish and pork is what the child will eat, try making a stew from the chicken and pork, adding veggies like tomatoes and peas and potatoes.
Sometimes a veggi can be disguised as something else. For instance, I had a foster brother that was five who wouldn't eat squash opr potatoes, but he loved fiosh.
Mum would fry it up in olive oil, covered as if it were fish, then tell him it was fish and he would eat it up, never questioning why it tasted different. If mom said it was fish, it was fish.
The same for stews or soups. If it was beef stew, she told him it was chicken, etc.
Also, if the child is old enough, get some children's vitamins for her, this will help cover any deficiency in the current diet.
Their tastes will change over time, so don't get frustrated.
GL!