I am a Realtor working with lenders in and around the Manassas area and have recently learned of some programs that require a credit score of 620 and require 0% down. Because some of Manassas is considered rural area, you may be able to qualify for a USDA loan with the above credit score. There are some income and limits as well, but feel free to Google Virginia USDA loan programs. As with all finance programs, they can be complex, so you can't rely on Google to give you the full picture. If you're still trying to purchase the home and need assistance, please feel free to contact me. I'd be happy to get you in touch with a loan officer that is familiar with all of the local area programs.
Exit Heritage Reality
15030 Washington Street
Haymarket, VA 20169
Cell 571.393.1766 (call or text)
Office 703.753.9100 ext.313
If possible, you might consider having your grandmother provide you with seller financing as well. If she agrees to financing, you could use the 10K downpayment and she would dictate the terms of the loan. After a year or so, you may be able to refinance with a regular lender or bank and then pay her off. Not knowing the specifics of your situation makes it a little difficult to give any other information.