How to get my vassal to release prisoner

[Fishy101]

So I gave my sons duchies. My second son died young leaving his only daughter as heir. My heir goes to war with her to claim her title. She has no troops or income since she controls a newly conquered county. I tried to help by giving her gold but she did not hire mercenaries. This might also be due to the fact that there is a real shortage of mercenaries in this game for some strange reason. She is saved when my emperor died and my heir takes over. But then a relative started a war to give her title to another uncle of hers. I tried to help her by giving her gold. It didn't seem to help so I gave her another newly conquered county. That didn't help either. Eventually she loses and has her title taken from her. She is also imprisoned. She has been imprisoned since before she was an adult and now she is in her mid 20s. What's worse is she is in the oubliette. Her heartless uncle won't release her and I can't make him. I am now upset enough to do whatever it takes to break her out. But her uncle has no bad traits. The regular pope won't excommunicate him. My antipope who I installed so I can change my religion has lost his ability to excommunicate or lift excommunication. Apparently he has been antipope too long. What can I possibly do to rescue her?

 

[Fishy101]

From the response, I take it that short of straight up revoking his titles all the way till he has none, there is no way other than cheating to get my niece out of prison.

 

[Sopot]

If she is a title claimant, then she will probably never get out of jail.

 

[yezhanquan]

I've seen one vassal inherit a kingdom, and still remain in the dungeon until he died, as a king.

 

[Fishy101]

If she is a title claimant, then she will probably never get out of jail.

Ya, she's a claimant since he usurped her title.

 

[Fishy101]

I've seen one vassal inherit a kingdom, and still remain in the dungeon until he died, as a king.

That's pretty depressing.