I don’t know where we went wrong

My oldest child (just turned four) slapped me in the face tonight. Like full on pulled her hand back as far as possible and hit me with as much force as she could. She’s been just awful lately with stomping around and slamming doors and just screaming multiple times a day over minor things (like having to wait until I’m done showering to get her snack) but tonight just broke me. I started crying and she laughed at me, she thought it was hilarious. I don’t know where we went wrong. We don’t spank her, we talk to her, we use time out if we have to, but her behaviour is getting worse and worse. I feel so sad.