Just spoke to nram. I can't take her off the mortgage as I cant afford repayments going by a income expenditure form even though I have been paying it.
How long is the mortgage for? I mean you've been paying for 15 years so what do you plan to do in say 5 or 10 years when it comes to an end and all you've done is pay off the interest?
If you've been living there then it is perhaps right you have been covering the interest payments. Have you had a valuation recently? Why not get a third party to come and value it, perhaps get her to arrange this rather than you so it isn't just you fobbing her off and she can get someone else giving her an opinion on what it is worth and in turn what her share of the equity is. You might then be able to postpone selling it for a bit.
You mention your wife is "fingers crossed going to uni later this year"? Why not postpone that for a year and solve your problem. If you can't remortgage now because you don't earn enough then get two incomes and re-mortgage. You could pay off your ex's share of the equity (if there is any) and perhaps more importantly for her, if the whole reason for this was for money towards a deposit because she intends to buy, she gets taken off the mortgage and it is then down to you and your wife.
You still need to figure out what to do re: repayment but at least you've got this immediate problem solved.