My wife's mother in her 60s got a US tourist VISA approved back in March with little issue. Her wait time to get an interview was nowhere near 305 days. Was about 100 days from the time she submitted the application. Maybe the wait times are longer in Hanoi then Ho Chi Minh. Mother owns a house in Ho Chi Minh worth about $700k with the father, has a lot of family in Vietnam, but no pension or retirement income (sounds pretty similar to your situation actually). Her mother used a company over in Vietnam to help her with the VISA process. I ended up writing a letter to support her visit.
On the other hand, my wife's sister who is unmarried and in her 30s, has a job but owns no property, tried to get a VISA 6 months ago to visit my wife and was denied.