It all depends on whether or not it is seen that she has contributed to it. As she has lived there for 12 years she would in law be deemed to have an interest in the property. If you have pooled your incomes etc since being together i would presume that you each have a 'share' in any potential equity.
Melanie Nicholas 28 years insolvency experience - 23 of which in the Insolvency Service - Insolvency Manager Jones Giles