Young relative(20 yrs old) is on life support and is brain dead, what are her chances of recovering?

Roughly the same you will be Appointed King or Queen to England.

That means none... brain dead is as bad as it gets. Basically no electrical activity in the brain.

There is almost no chance, if you are religious pray to your god.

There is no chance of recovery once there is brain death.

I'm so sorry that you and your family are going through this. Brain dead is unfortunately not something that you can recover from. There is no brain activity. The brain cannot regenerate itself. Brain dead is brain dead, and a lifelong condition.

The good news is that she's likely not in any pain, and has no idea what's going on.

The bad news is that whatever life she has left will be on life support with no chance of recovery.

So sorry.