@toomanylols It will be a bit hard because she has gained bad habits and certainly a taste for certain food, but if you are consistent and determined, you will succeed .
It is not only the food on the plate but the whole eating routine that you should address, for both of you. Kids learn by example, so you should eat together, sitting down at a table with plate and cutlery.
Clean your cupboard and get rid of all the junk and processed food, starting with jelly. Jelly is the most infamous invention and nobody should eat it. It is a dead animal carcass that is boiled until tendon, skin, bones, cartilage and other inedible body parts are melted into a gelatinous mass. It is utterly disgusting.
Even "healthy" food that is highly processed and transformed should be ditched. Cook real food, that is fresh and colourful.
Breakfast" oats or a wholemeal toast or better sourdough bread
Lunch: a small steak with green beans, a sole with some boiled potatoes, a chicken breast with sauté broccolini, meatballs in tomato sauce with brown rice, two hard eggs with some spinach, swordfish or mussels if she likes them with a lettuce, a meatloaf with roasted pumpkin, ....
Dinner : pasta, risotto, soup, lentil stew, a curry, a dahl, and some vegetables, grated carrots, tomato salad with onion, hummus and celery, .....
She can have fruits for snacks.
Have a frank discussion with your family and tell them you don't want her to go through the same ordeal as you and that you want to start changing the family eating habits and that they shouldn't sabotage your plan.
Sweets and other birthday treats are just for birthday, and artificial food such as crisps, rice cakes.
Of course, from time to time, she can have chocolate or a piece of cake, but real one, quality ones.