Look up the terms on which student loans are provided by the UK government (see http://www.slc.co.uk/). Basically, the interest rate is the rate of inflation, and repayments begin only once a certain salary level is reached and are proportionate to salary. After a certain period (I think 10 or 15 years), the loan is written off.

What I’m suggesting is that you offer to fund emulation of these terms, working out what she would be paying each month based on her income under these terms, and making up the difference yourself to the actual repayments. If you do that, it will take a lot of the pressure off her and give her a chance to sort out what she is going to do, without actually lifting the whole responsibility away from her. If this suggestion seems overly generous to you, remember that you are co-signatory!