This person needs to buy out your interest in the house by refinancing you out of the mortgage. She/you need to talk to the lender about the need to get you off the mortgage and have her take over your interest. If the bank is willing to do this, they would need to refinance in her name only and you can give her a quit claim deed of your legal interest in the home. If there is significant increase in the value of the home since you purchased it, you may want to negotiate a payout for this quitclaim interest of the amount of the increase in value, or you may decide that it is just good enough for you to get off of the mortgage and agree to do so if they drop you from the loan.
This can be a difficult problem to resolve. When this problem exists between married people, it is usually resolved in the Divorce process. However, when people are not married, there is no specific legal procedure to address the situation.
If the property is worth at least as much as you owe currently, and if your partner has sufficient income to refinance the current mortgage, that is one possible solution; if you deed your interest to her in return for her obtaining a new mortgage in her own name, that removes you from the deed and the mortgage. If the property is worth more than the mortgage, such an agreement should also provide for her to borrow enough to pay you for your share of the "equity" - the difference between what the mortgage is now and what the property is worth.
If it is not possible to reach an agreement with her, your only other option is litigation.
If you have moved out and she refuses to pay rent or sell the house, then you can maintain a lawsuit to partition the property. The property would be sold publicly, any reimbursements (for example, if you pay the mortgage or taxes or repair bills, those come off the top) and the costs of the sale are paid, and then the balance is divided equally. She would be charged with rental value from the time you move out.
This is expensive. The lawyers will take the lion's share of the proceeds. But because you did not enter into a written agreement before you bought the house, there is no alternative if one partner decides to be a stupid lout.