Here's the answer, lifted right from the VA web site:
The unmarried surviving spouse of a veteran who died on active duty or as the result of a service-connected disability is eligible for the home loan benefit.
If you wish to make application for the home loan benefit as a surviving spouse, contact our VA Home Loan Eligibility Center. Or, you may call the Eligibility Center's toll free number, which is 1-888-244-6711.
In addition, a surviving spouse who obtained a VA home loan with the veteran prior to his or her death (regardless of the cause of death), may obtain a VA guaranteed interest rate reduction refinance loan. For more information, contact our VA Eligibility Center.