Celica fan checking in. She's my vote for tomorrow. Okay, so first and foremost, this'll be going into late-game SoV spoilers but I'm not gonna butcher it with spoiler tags, so be warned, folks.
Celica, given the information she had available to her, absolutely made the sensible choice. A lot of people say she was dumb for "trusting Jedah," when in all actuality she never did. Her decision wasn't birthed from naivety, but rather hopelessness. A lot of it involves looking at the situation from Celica's point of view.
Celica, most importantly, is a priestess of Mila. As such, it's expected that she'd know the ins and outs of the faith. Mila herself is a divine dragon. According to the established lore of the greater Archanea/Valentia universe, the dragonkin are prone to degeneration: eventually, they'll deteriorate to the point of losing their sanity and going on a rampage. This isn't something that's a hidden fact in-universe. Malledus and Marth bring it up at some points in Shadow Dragon, for example, so someone like Celica, who worships Mila, would undoubtedly know this.
Likewise, though, Jedah would also know this, as he is the high priest of the Duma Faithful. He's the one who mentions that Duma is going mad to Celica in the first place. Jedah would gain nothing from lying about Duma's madness in this case, as it's a scenario that would likely get him killed, as well. It's an incredibly severe issue. As well, Halcyon and (prior to her conversion) Silque both show that those of the Duma Faithful aren't necessarily evil.
But more importantly, the only reason Celica goes to Rigel in the first place is to save Mila, who wasn't in her temple. Mila's Bounty is the only thing giving life to Zofia, and without it, the land is infertile. Famine and drought will continue to plague her country until it is no more. So Celica follows Jedah to Duma Tower because listening to him is literally the only chance she has at saving Zofia. She knows Zofia can't sustain life otherwise.
So then, ultimately, comes the big reveal that Mila sealed Falchion away within her skull. Again, if anyone, Celica would know full well the implications of this. The Falchion, forged from one of Naga's fangs, was the dragonkin's last line of defense. If they were to go mad, the Falchion could kill them before they kill everything else.
...And Mila sealed it away with her in her death, leaving Valentia without a fail safe against Duma's own degeneration which is already taking place. From Celica's viewpoint, Mila has essentially forsaken her people. She left them to die. The reactions from Clive, Clair. Lukas, Gray, and Tobin later on reaffirm Celica's fear. In universe it's a well-known fact.
So that's why Celica offers herself to Duma...she had no other choice. Her other options were taken away, so she was left with only the choice of sacrificing herself. That way, at least there was a CHANCE Jedah was right, and that there was a possibility her death would save her people.
The other thing to point out is that Celica has no reason to believe Alm is able to unbind the Falchion. As players, we of course know that. But at this point Celica doesn't even know Alm is a member of the Rigelian royal family, so there's no reason for her to think this was possible.
Naivety isn't Celica's character flaw. If anything, her fatal flaw is her martyr complex, her willingness to give her own life for the greater good. And even then, she's an incredibly caring person, and fulfills her duties to her people despite being in hiding. She doesn't seek praise, but righteousness. She's pacifistic, but powerful in her own right. And when the time came for her to accept the crown and truly become Zofia's Princess, she did so, and in doing so made the hardest choice she could have made: the choice to give her life for the slim chance of giving her people the life they deserved.
So yeah. That's my input, anyway.
