I've a 2.5 year old too so fully sympathise -they can certainly test you to your limits!
Children need rules & boundaries and your DD is testing those, seeing how far she is allowed to go.
Your biggest challenge is staying calm, keep your voice low and slow (SO guilty of not following my own advise many times but when I do it works better)
When you ask her to do something -what's in it for her? She's thrown her food on the floor...why would she want to pick it up? I don't mean use bribes but try and pick your timing and phrasing.
For example -getting my son to put his shoes on, NO point telling him to do it while he's watching Fireman Sam, it just won't happen.
So I wait for the adverts and then ask if he can find his shoes as....uh, oh we've lost them! (We haven't) And then try and relax, make a game of putting shoes on, say "do you know how to do velcros?"
(This does NOT apply if in a hurry - I admit to using the demonic voice then! 😂)
If she throws her food on the floor she's obviously not hungry so end mealtime and explain why. Move her to another room (no screen time!) and tell her to sit down and calm down. Then walk away.
A lot of their actions (throwing, screaming, etc) are to get your attention. Say a very firm 'no', move them to a calm spot to amd then walk away yourself.
Does any of that make sense? I am only reeling off what I do weekly and seems to work. Keep in mind they do have Monster Days and I'm learning to just ride those days out.