Translation:What happened once she got off the train?
"What happened once she got off the train" is literally the official translation. If it wasn't accepted file a bug with the developers, the contributors can't do anything more.
However, you may have answered "What happened once she got off of the train?", that is a bit different. At least we have a very recent report like that.
"když" is irrelevant.
The perfective aspect in "vystoupila" means the action is completed, so it cannot be "at the time that", it must be "immediately after the action was completed"
If we used the imperfective "když vystupovala", the action would be in progress and it would hence mean "at the time that"...