If you and your girlfriend (or exgirlfriend or whatever the case may be) are on the deed as owners and you both took the loan, she can't assume the mortgage unless the lender approves her assumption. If you're removed from the deed, this will activate the "Due on Sale" clause that are typical in 99% of all loans.
If anything in the deed changes, in most cases, this will trigger the "due on sale" clause and the lender will be notified as soon as something changes in the deed, so be very careful. Although in the state of New Jersey, an attorney is not required for any real estate transaction (It is a misconception that you need an attorney in the sale of residential real estate), it is strongly advised that you consult with one if you can afford it.
The time frame is as long as the lender will provide your girlfriend to either refinance or change the loan over to her as the sole borrower of the loan. Remember that when you both got the loan, there was probably two salaries that the lender considered in approving the loan, now they have to consider that only one person will be paying the mortgage loan.
If you can't afford an attorney, you both have to talk directly to the lender and see if they can provide a solution to your situation.
Good luck and all the best.
A Home For Sale Realty