I'm not sure if this is normal behavior for a 4 year old

by Dawn
(Louisiana )

Since my daughter has turned 4, she has become a completely different child. She has meltdowns over everything, she has become defiant, she has nightmares and she even hit a child at school :(

This is not my daughter. I need to know how to help her or if I should seek help for her. The meltdowns are uncontrollable. It takes forever to calm her down. Once calmed down, she acts like it never happened. Almost as if she doesn't remember.

She is an extremely brilliant child. Her little mind is incredible and smart.

She started preschool a week after she turned 4. I have gotten so many calls from school because she is having a meltdown. I just don't know what to do anymore.

Threatening with punishment does not work. Giving a goal to work towards worked for a while. Giving her ways to cope with her feelings (take a deep breath when you get mad) worked for a while. I'm so out of ideas.
Help. Please.