How can I help my 4 year old use her words in times of emotional distress?

My 4 year olds preschool teacher had a talk with me about my child, saying that yesterday at school she wailed and cried over every little thing. She said she was clingy and not following directions. I am a single mom and sometimes get fed up and irriatated with my child. I know that I have to be a good example for her but sometimes is hard. I'm also depressed and think she may catch onto it. How can I helpher talk through her problems and help her use words when she is upset instead of crying at every little thing? Nothing drastic has happened at home lately...I keep thinking it may be her allergies, lack of sleep or something else bothering her. Any advice please?