What can I do about this situation?

Need advice please! As a single mom of two, I really try my hardest to keep it together in front of my kids. Unfortunately, about four weeks ago, maybe five… My four-year-old daughter seen me lose it on her dad. She had never seen me and her dad fight before. Anyway long story short, I flipped out on him because when he tried picking her up and he was under the influence. (We met at a near by Walmart) I obviously didn’t let her go because he reeked of alcohol. And At first, it started off like are you serious? (No yelling) You would really try to pick up your kid under the influence? Like he should have known better. Anyway, I was hurt and mad, he of course tried to deny it which sent me over the edge because I was already stressed out from other things. I yelled at him and was crying. Again, she had never seen me that way. After all that happened of course, I apologized and tried to explain the situation the best way I could. We went home that was the end of the story. Fast-forward to now, anytime she hears me on the phone talking with a firm voice not yelling, she just follows me and then asks me if I am upset or mad. It truly hurts my heart that she feels that anxiety because I personally went through it growing up with my mom. The only difference is there were a lot of angry outburst in front of me. This literally only happened once, and I’m not downplaying her feelings at all. I just want to know what to do from here? It hurts my heart so much that she worries if I’m mad or upset just because I’m talking in a firm tone and it could be with anybody. Obviously that situation really traumatized her and I want to help her get past it and I don’t want her to feel scared or walk on eggshells. Any advice would be appreciated! And please no bashing, I’m pretty sure we all have lost it once or twice.