Agree that the student is not ready for college with this level of social anxiety. She needs counseling, and probably so do her parents. This family has some seriously unhealthy relationship issues.
Social anxiety can be disabling, and it appears that is the case here. Get this girl some help. Her parents don’t pay enough attention to her condition to know what level of stress she can manage, and they haven’t given her the right help to learn how to manage everyday levels of stress. Deal with it now, the sooner the better.
And yes, she should write thank you letters and apologize. I recommend her mother help her draft the letters, and apologize profusely and sincerely to her for putting her in this situation.