A loan is a contract and the law of contract says there has to be a clear agreement between the two parties as to a repayment plan. This could be 'when I finish my degree' even (but if he doesn't finish his degree, he will never be expected to pay the loan back legally). A vague expectation will never stand up in a court of law.
However, even a verbal agreement will stand up in court.., but in this case it will be their word against his as I doubt he'd state he agreed to pay the money back.
As said previously.., if its cost her £2k to learn a hard lesson., and that this person is a skunk.., its a lot less than a longer relationship with him would have cost her (seriously I am speaking from experience here.., try a 12 year relationship lol).., altho I am sure that is small comfort.