I get very embarrassed when my 4 yr old daughter just ignores people and don't say hello.

Sometimes it feels that she does it on purpose just to make us mad!

I guess this was a new question? You posted this as an answer to a several year old thread.
So assuming this is a question, not an answer, I have moved it here.

*** the child is 4, she will ignore, people, she will ignore you, of course it is on purpose sometimes, other times, she is just living in her own world at the time