@leahmaysimmonds sushi is rice.
Stop giving - if she is having them - all industrial baby ultra processed food, from rice cakes, to melty puffs, vegetable crips and other cereal bars, rusk, wafer, ....
in order to not make the problem worse upstream, and downstream, since you have tried many things, give the osteopath a go. Have one session and see how it goes.
DS2 had terrible reflux, ended up several times in hospital for aspiration pneumonia when he inhaled his vomit, and I was given a very long list of food to avoid for both of us (I was BF) and it included poultry, not only the eggs, but also the flesh of poultry, so no chicken, turkey .
It was a no citrus, no tomatoes, no dairy, no wheat, no poultry. What does your GP say? Did they recommend some food and told you to avoid others?
Try it. Have oats for breakfast, or some avocado on spelt toast (I made my break) , a soup with a spoonful of lentils for lunch, a few bites of cod for dinner
Fruits, cooked or raw in between. It is summer, watermelon helps a lot with constipation. Yellow kiwis as well.
Just avoid the ultra processed foods aimed at children but also adults.