how long can you be dead for without even getting brain damage?

For each minute your brain does not receive oxygen, Your chances of living get reduced 10%. So in about 10 minutes a person's brain can live without oxygen. There have been cases of cold water immersions (drownings) where people were under water for a very long time, like almost an hour, and they were revived with no long term problems. Those cases though were in extreme cold.

I believe in miracles, I believe God can do anything. So you have to decide what you want to believe.

Medically, it's very unlikely. But if you have faith, anything is possible.

When breathing and heartbeat stop, the first organ affected by the lack of oxygen is the brain because it uses more oxygen than any other organ of the body, and without oxygen, the brain deteriorates rapidly at normal body temperature. However, when cooled down sufficiently, such deterioration slows quite a bit, and people have survived being under very cold water for about an hour because their bodies got cold enough to almost stop deterioration.

Actually after 5 minutes without oxygen to the brain damage can occur, the longer without oxygen the more damage. I highly doubt your friend was dead an hour she would have some brain damage if that were the case

The medical definition of death is the cessation of brain function, not the stoppage of the heartbeat and breathing.

Google "brain death".

Like Kimmi said have faith and believe in God.