Fiancé living in my house

I own my home , 15 years left on the mortgage. My partner has moved in and makes a minor monthly contribution to the house hold. She has been able to accumulate savings from the difference in the rent she was paying and what she contributes now. Long term she is going to get a house / home without the expense. Should I leave things as are, or would it be fairer to ask for a lump some to get equity in the house or should she pay a fairer amount each month ?