I'm sorry it's being so stressful! Just think of her as a baby, only a lot bigger because that is what her comprehension is like right now. She knows how to express her feelings, but she has no restraint really at this age. (So know that it's not because you are a bad mom or anything!)
When she hits, gently take her hand and have her be soft and pat whatever/whoever it was she was hitting, while saying "Be soft. Good job! You're being soft!" That way you are praising the proper behavior and giving it a lot of attention, as well as redirecting her...and you are giving no power to the negative behavior. She's not going to understand if you get mad at her for hitting, and she'll likely start doing it to get a reaction from you. So, give the hitting no reaction, teach her the proper behavior, and give her lots of attention for that works the best in my experience. It doesn't mean the behavior will immediately stop, but it definitely improves.
One thing I have found to be very true for this age, the more you try to punish or get angry at them, the worse they will behave. So, try really hard to approach it from a positive angle.
As for her yelling while being upset, she's only 20 months old. Totally normal. I personally wouldn't do anything about it except maybe try to comfort her and calm her down. That doesn't mean she gets what she was wanting - it just means you can care about her feelings and her lack of understanding about it all. If she doesn't react well to a calming reaction from you, then you can leave her be or move her onto her bed to scream - not in a mean way - just in a way that you can't yell and scream and disturb everyone. If you need to do that, your bed is a good place. I don't believe in teaching kids to never express anger. I believe in teaching them HOW to express it.
As for her throwing her spoon, again, think of her as a big baby. She doesn't have the understanding of an older child. I'm guessing you took the spoon away? That's about all I do when my child starts doing that. If they are no longer interested in eating and look like they are about to toss things, I take it away. Or if they throw it before I realize they are done, I take it away and feed them myself or let them down if they are done.
I tend to be pretty easy going when it comes to my kids that age. I do a lot of redirecting, practicing proper behavior, and giving attention for the correct behavior. I think life will be much easier if you allow for the age and don't stress too much over normal behavior for the age. Doesn't mean you don't teach the correct behavior (like mentioned at the beginning of the paragraph), but just know that kids don't behave perfect and it takes time to teach.
Your daughter sounds completely normal. All four of my older ones could easily be described the same way:-) My fifth is a newborn, so we're not there yet, but I imagine she will be.
Hang in there!