She is saying that she wanted to say something, but she didn't have the courage to do it and she wanted to say it really bad. She would never talk or say what's on her mind, basically she is afraid to speak up and tell anybody what she's thinking.
She used to be shy and wouldn't say anything if she thought someone is wrong.
He wrote it with reference to "Another Brick In the Wall" by Pink Floyd. Stifled by rules and waiting to exhale honestly.