Alexa wants to use indirect proof to prove that all rectangles are not squares. She first assumes that all rectangles are squares. Alexa then provides the following counterexample to disprove her assumption.
She concludes that all rectangles must not be squares.
Which statement best describes Alexa’s indirect proof?

A. Alexa's proof is incorrect. She followed the steps of an indirect proof in the wrong order.
B. Alexa's proof is incorrect. She made an error in her counterexample.
C. Alexa's proof is correct and contains no errors.
D. Alexa's proof is incorrect. She made an error in her assumption.