Vita had originally said the "blessed child of god" would bring eternal happiness to the empire, but in the first timeline, the empire crumbled due to Zena and everyone (including Zena) lost.

Remember that bestowing a name on Tia is equal to making Tia a blessed child. Since that day Tia can hear the voice of God (she hears all the prophecies that God is sending to the priests) and that puts her on the same level as Jieun. Jieun can heal flowers (but not humans because her powers are incomplete) and Tia can hear Vita's will. That makes them both blessed children of Vita.

Vita's prophecy is not as clear as what we read in the manhwa. Vita just said that her blessed child would be born and would bring peace and prosperity to the empire. Jieun likely never was meant to marry Ruve, for when she married him, she brought destruction and tyranny to the empire. But when she saved Tia and allowed the capture of the villain, she fulfilled the prophecy : Ruve was able to marry Tia, and they had a son who became the greatest emperor of all times.

My personnal interpretation is that the first timeline was necessary for Jieun to know who the true villain was and return to 2nd timeline to help catching him. And her being blessed by Vita, her incomplete powers that couldn't heal humans, were meant for her to exchange in return for Tia's life.

Jieun gave all her divine powers in exchange for her wish to save Tia's life, and her black hair turned white. That is the mark of people who abandoned their blessing. So yes, she is not a blessed child of Vita anymore.

In the second timeline, they all lived happily ever after, except Zena and ji-Eun. Since Ji-Eun gave up her powers, Tia is the only "child of god" in the second timeline.