Check Out Your Friend's Credit
Make your co-buyer go through the credit makeover process to maximize her score, too, then consult with your mortgage professional. Even if your score is below 580, you might not need to wait if your co-buyer's score is the one lenders want to see. Generally speaking, the buyer who makes the most money is the one whose score is of interest to lenders. Of course, the person with the highest income is also often the person with the most bills and, accordingly, the lowest credit score. Consult with your mortgage professional to see whose score is important.