Quite right. The GMC's guidance can be found
here.
Illustrating the threshold of student fitness to practise:
Has a student shown a deliberate or reckless disregard of professional and clinical responsibilities towards patients or colleagues?
An isolated lapse from high standards of conduct - such as a rude outburst - would not in itself suggest that the student's fitness to practise is in question. But the sort of persistent misconduct, whether criminal or not, that indicates a lack of integrity on the part of the student, an unwillingness to behave ethically or responsibly, or a serious lack of insight into obvious professional concerns, would bring a student's fitness to practise into question.
However... this particular student has done more than just "a rude outburst"...
Has a student behaved dishonestly, fraudulently, or in a way designed to mislead or harm others?
The medical school should take action if a student's behaviour is such that trust in the medical profession might be undermined. This might include plagiarism, cheating, dishonesty in reports and logbooks, forging the signature of a supervisor, or failing to comply with the regulations of the medical school, university, hospital or other organisation.
So I agree, probably not for the GMC, but I would certainly inform her clinical/educational supervisor, and in this case, maybe the medical school dean as well.