Yes, 4 years old is hard.
As much as it is hard for the Mom... it is harder for the child, because, they do not have full capacity or awareness or knowledge of things/the world/moods, like an adult has. Nor do they have "coping-skills" either.
Their emotions, are not real fine tuned or developed yet. So keep that in mind. They don't even know the succinct names for their exact feelings, nor can they even fathom or analyze their own feelings or WHY they are feeling that way, nor... do they have full problem-solving skills nor do they have deductive or inductive reasoning, yet.
So, yep, they are having a hard time at this age.
Plus, coupled with the fact that at this age, everyone... "expects" them to act and be, all grown up and a "big girl" or "Big Boy." But they are still very young still.
So the adult expectations of them, plus with their own development, it clashes. Frustrating for the child, then the parent.
Teach your daughter, how to express herself and tones of voices. Make it fun. Teach her the names for feelings, and that there are MANY ways to solve it and to feel better etc. I have a son & daughter, and from 2 years old I began teaching them those things. Then at only 3 years old, my son for example, could tell the difference about his feelings and he knew the difference between him being "grumpy" or "frustrated" or "irritated." And he'd tell me. I told him even Mommies get those feelings to, so just tell me, in a palatable way. And he would. THEN he would even tell me "Mommy, I'm grumpy, I'm going to to over there to be by myself..." and he would. Then a minute later he'd come by me and say "I feel better now..." and hug me.
I was proud of him.
And likewise, when *I* am grumpy or in a bad mood, I will say that to him but not blame him. And I tell him "Mommy is grumpy right now, but am trying to keep pleasant..." etc. And that teaches the child too.
I never punish or scold my kids for their feelings... unless they are ON purpose, being difficult. So the parent needs to DISCERN, that. IF my kids are honestly just feeling icky and grumpy for innocent reasons, I help them. I do not scold/punish for that. Because, I want them to know themselves and that they can come to me. And also because, no Mommy is perfect about moods either.
But yes, this is a hard age.
Common.