What does she mean by "I feel ten feet tall"? Is that a common metaphor?

Native speaker’s answer
Rebecca
Yes, this is a commonly used expression! When you feel proud of yourself, you feel tall and big. That's where the expression "to feel ten feet tall" came from! You can use this when you feel proud of yourself for something. Ex: I made it into my top university choice with a scholarship. I feel ten feet tall right now. Ex: I feel ten feet tall right now, my professor just complimented my project in front of the entire class.