Yeah, Life & Death pre-pack patch added the feature where the children taken away will not be deleted but instead appear in Manage Households. Children that were taken away before this patch are still deleted though and there is no way to get them back without recovering an older version of save. So yeah, recreating her as a young adult is the only way.
In addition, at one point, deleted sims (whether it's by being culled, released to netherworld, old version of being taken away by social worker etc) will only retain their last portrait, name, and place in the family tree (relations). This is sometimes important to know as if your sim already had two parents, you cannot create new ones in CAS even after the original ones are deleted. The system is shaky though, as sometimes patches may delete deleted sims from family trees (this has happened to me).
Good to know kids will no longer be deleted. This girl was taken away 8 RL years ago, so she was a lost case then.
