I could not reproduce the problem. Here is what I did:You should always be able to add the captives to council from once you get them. So I guess that is the bug you're running into.
It would also make it much more straightforward if this quest was not available until you'd already taken them to the palace, because it can only be completed there. Maybe this is the intention but it should be implemented.
1. Started the game.
2. Parleyed with Angilia.
3. Played the Oryeonguk quest (this is essential although Skip 'n Win also works). Just don't attack Oryenguk without completing the quest one way or the other.
4. Conquered Oryeonguk.
5. Sent Angila to the dungeon and bred her.
6. Waited until her Act 2 became available and played it.
7. At the end of her quest I sent her to the palace.
8. Fully built Oryeonguk.
9. Went back to the palace. The option "Check how grateful Angilia is" became available.
Things you might have gotten wrong:
1. Attacked Oryeonguk without playing (or skipping) the quest.
2. Did not re-build Oryeonguk.
This code was not touched in about two years I guess, so it's hard for me to image how a bug could crawl in there now (although bugs can get creative).