Sounds to me like the student has a mental health problem. My duaghter has a mental health issue and she can be difficult and confrontational to people if she perceives, in her distorted way, that the other person is being mean, or angry, etc. The other person is almost never being mean - but my daughter's perceptive skills are just off kilter.
YOur professor needs to talk to the department head, provost, academic advisor or dean of students to find out what the school's policy is and then defer to that. I cann tell you that people with mental healt problems have as much difficulty as those with diabetes or cancer - and perhaps more becuase of the stigma they can't just blurt out that they're bipolar or ahve borderline personality disorder... College age is when many people initially present with psychiatric issues if they end up with them. Unfortunatley, it's really difficult to ask the student or the parents if this is the case! Which is why I suggest going to a higher level.
For my daughter I've learned that most kids with her disorder have less issues as they get older (not the case with all mental helath problems) but most people with disorders are highly intelligent and so college is a good thing except for the stresses - academic, emotional, interpersonal, etc. My DD will be in college in 2 years but she knows she will be commuting and not going full time so she can have her family support system intact.
Good luck professor husband!