The house is still pledged as collateral against the loan by the BF
So its the same basic process as if they both were on the deed.
The house is at market value eg 500,000
The loan is MV-60k
(Assuming the bank dont lend on other costs)
BF owes bank 440,000
DD owes bank 440,000
Each debt is only reduced by the total repayment (+interest)
And the bank can collect the full amount from one or both.
If BF is not paying bank write to him asking to make payment
Plus as BF is not paying the bank write to DD looking for the full monthly amount.
Bank warn both that breach of contract will result in the full amount falling due and that they will repossess the house
Bank add on penelties and give them a chance to reorganise if they can prove stoppage is temporary
If BF And DD are still not paying and the bank instruct him to sell the house for the minimum of the loan amount plus any other charges.
And warn her she owes the full amount (with no house to cover or part cover the loan)
Neither paying and house not selling so the bank go to court to get their money.
If DD has 440,000 cash they look for the cash and BF keeps the asset.
If no cash is offered they request an order to seize and sell (and add in the banks costs) to recover their money.
Plus get a court ordered repayment plan against both if the MV will not cover what is owed.
The judge will look at the individual circumstance around ability to pay
So owed 440,000 +30,000 legal etc
House needs to clear 470,000 made 400,000 and BF filed as a bankrupt
DD can be ordered to pay all 70,000 and a charge can be attached to any property she owned and the bank could look for a sale order.