You cant use a lvl 30 Isra from prison since she didnt get exp necro as last skill. And it makes good sense too, since she is totally overpowered at lvl 30.
What annoys me is that you are not allowed to make any fights at all with her. The rules should be that you can make figths but you have to dismiss all skeletons gained from the fights. The purpose of the rule is that you shouldnt get to many skeletons, not that you cant make simple scoutfights.