Is the state of sadness and discomfort after performing Salatul-Istikhara, and the student's enrollment in a college that was not her first choice, considered a sign of displeasure with Allah's decree, and is it haram, or is it one of the signs of Istikhara indicating that this choice is not suitable?

The person performing Istikhara (prayer for guidance) should proceed with what they intend to do after the Istikhara, and Allah's success will be a sign of His choice for them. We advise you to strive diligently in your current studies and be content with what Allah has decreed, and not to transfer to another college and waste your life. Consider Allah's pleasure and what is more beneficial for your religion and worldly life, and what keeps you away from Islamic prohibitions. If both colleges are equal, or if your current college is preferable, then continue in it and seek Allah's help. Your continuation in it is an act of filial piety towards your father. What happened might be due to envy, so seek help through Ruqya (Islamic exorcism/incantations) and prayer for success in what is good.