They have quite small tummies so tend to eat small portions with a small snack in between meals - e.g. a plain biscuit or some fruit or a few cubes of cheese.
I used stock cubes in cooking but I wouldn't give something that's obviously laden in salt like a bag of crisps.
Think about the size of treats in proportion to her body size and don't give them just before a meal.
With fish, i just fork through it to make sure there are no bones e.g. with a bit of salmon. Fish fingers are usually fine i think.
Soft food like tender meat, fish, pasta, cottage pie - all sound good. I wouldn't give mine a lump of steak for example because she'd give up on chewing it.
Just get some childrens' yoghurts in and a small amount of mild cheddar would probably go down well.
Drinks- maybe ask what she usually has because it varies a lot with people. Mine had watered down squash but a lot of people don't like their dc having it. Some just have water or milk or watered down fruit juice.
I wouldn't give any dc that wasn't mine nuts - just in case. Allergies can start at any age and the nuts one can be very serious. Although unlikely I just wouldn't take the risk.
And just be aware of the choking hazzard. Chop food up small, just to be on the safe side. We were asked at pre-school age from 3 to 5 to still halve grapes and cherry tomatoes.
Get in the habit of having all food and drink including snacks at the table as even a dry biscuit will get mushed into your furniture otherwise.
The sort of thing mine ate at that age was jacket potato, spaghetti bolognaise, risotto with just a bit of chicken and a few peas, omlette, macaroni cheese, casserole and mashed potato, salmon and veg, cottage pie. Perhaps a sandwich for lunch. Puddings would be a petit filou type yoghurt, jelly with fruit, or just fruit or perhaps some custard.
I hope you have a lovely time. I'm sure she'll let you know if she doesn't like something.