After (as) Taramiel I go to warn her friend and she tells me to go away, I get stuck.

The game indicates me to go downstairs but when I do that I get locked behind a gate and I can no longer go upstairs.

Please help me I have been stuck on this for a really long time and would really appreciate some assistance.

As Taramiel you're not supposed to leave the Underdark. There should be a place where you can teleport to the cell where the boy is being held prisoner...