Toddler understanding

I have an almost 3 year old daughter. Very smart. Knows everything BUT she cannot express herself or have a conversation. If she cries for whatever reason and you ask her what happened, she just repeats “what happen, don’t cry, it’s okay”. She can’t tell you why she’s crying. You can tell her some commands and she doesn’t seem to understand what you’re telling her and would likely burst out crying. She’s progressing but slowly and only a few things. I try to have conversations with her. I try to explain to her by saying one or two words when I know why she’s actually crying, like “it’s broken” “it fall”. “Want some …” I try to sit her on my lap and explain to her softly and slowly what I’m telling her when she thinks I’m fussing her for something. But I’m a bit concerned.