Getting Off the Mortgage

Getting "off the title" is simple.  You sign a new deed transferring your ownership to your sister and that's that.  Or the two of you sign a new deed transferring total ownership to her -- whichever, a lawyer can help with the simple process. 

 But getting "off the mortgage" is a lot more difficult.  You once signed a promise to be responsible for repayment of that loan, and you still are, even if you're no longer an owner.  Sometimes the lender agrees to release you if your sister can prove she is financially qualified to carry the debt on her own.  If they won't, the only way to be released is to pay the current mortgage off.  If your sister can get a new (refinance) mortgage in her own name, that would work.  If she can't qualify, you're probably stuck with the liability. 

When you want to take out a new mortgage on your own condo, your lender might agree to ignore the existing liability if you could prove (cancelled checks) that your sister has made the past year's payments entirely on her own.  I'll bet you don't want to wait a year -- your best bet is to explore this with your potential lenders, and with the institution that hold that current joint mortgage, and see if they have anything to suggest.