Do you know whether or not Yuna knew that the Guado intended to fire the rest of the party as guardians once she and Seymour got married? Seems like it would be a deal breaker for her even considering all the pressure she was under to say yes, from herself and the rest of Spira. Then again Seymour brought up being her Zaon and they way she said goodbye to the party before the crawler fight is a little ambiguous.
That’s an interesting question! And it has triggered lots of thinky thoughts, so let me make a cut.
TL;DR: I don’t think Yuna had thought it through very clearly: she was so focused on the confrontation that she wasn’t really thinking about her guardians at that point, as Seymour had intended.
This is a side effect of the power imbalance in her interactions with Seymour. I think all she was thinking about is what am I going to say to him? OMFG I’m planning to confront… a MAESTER?! That’s a 17-year-old girl challenging the Pope, or at least a bishop. It’s a gutsy thing to do, especially for someone who lived by the teachings. She was out of her depth. (She grew up quickly, though: look at her calling out Maester Mika during the trial and standing up to Maester Kelk on Gagazet).
Look at what Yuna says when she’s made up her mind to go meet Seymour in Macalania Temple:
Yuna: I have one question, if I may, sir.Tromell: My lady?Yuna: I want to keep journeying, even if I marry. Do you think that Maester Seymour would let me?Tromell: But of course, my lady. Lord Seymour wishes nothing else, I’m sure.
That’s an astoundingly submissive thing for Yuna to say. She’s spend years planning to sacrifice herself for this pilgrimage, she was determined to follow her father’s example, she’s been utterly committed to being a summoner, and then suddenly, she’s meekly asking if Seymour will allow her to continue her pilgrimage. As if it’s his call.
Holy hells, he’s manipulated her.
Seymour had stoked the same insecurities that caused Yuna to apologize to Tidus for being “overconfident,” as if it were her fault he’d blundered into the Cloister of Trials in Besaid. They were the same insecurities that caused her to ask Lulu, “I hope I did… okay?” in Kilika. She was starting to overcome those insecurities on the Mi’ihen Highroad:
Shelinda: But you don’t understand! The Crusaders won’t even listen to me. And it’s all because I’m just a lowly acolyte.Yuna: Don’t say that.Shelinda: (Gasp) Yuna: Well, I haven’t been a summoner for very long myself, you see. Still, I can’t put myself down every time I fail. People are depending on me. They’re depending on both of us!Shelinda: Yes! Yes, you’re right, my lady. Absolutely right!
But then Seymour came along and did his best to teach her the opposite of the lesson she’d just taught Shelinda.
Yuna: Why does he want to see me?
Yuna: What could it be? Oooh…¬[I hope] I haven’t done anything to make him mad.
We saw Seymour undermining her in every interaction. He opened the Crusader Checkpoint to her as a special favor, reframing her pilgrimage as a favor he bestowed on her. He told her that she was “too weak” and that “she can’t” fight Sin during Operation Mi’ihen. Afterwards, when she was traumatized by a massacre that would shellshock a generation of soldiers, he impressed upon her that she could only succeed as a summoner by taking him as “her Lord Zaon.” While she stayed up all night tending the dead and dying of that horrific battle, his words were probably playing over and over in her head.
It’s not clear that Yuna got any sleep from that time until Seymour summoned her to his mansion (the perfect stage to impress/intimidate her) in Guadosalam. There he dazzled her by showing her Zanarkand, the place she was making a pilgrimage to see, coopting Tidus’ promise to take her there. Maybe the rumors had already filtered back to him that she was traveling with a boy from Zanarkand (Seymour certainly knew who Tidus was later on, whose son he was and where he was from). Again, after overwhelming her with a powerful experience and reminding her that Yunalesca whom she was named for depended on Zaon, he popped the question.
He’d done everything he possibly could to knock her off-balance.
Dona, supposedly a bitchy rival, saw what Seymour was doing and told Yuna to try “standing on her own two legs” for a change. Unfortunately Dona also told her that she couldn’t rely on her guardians during the final showdown with Sin.
Seymour gave Yuna the same message, undermining her bond with her guardians, to the point that she hid Jyscal’s sphere from them and didn’t consult them. He’d even driven a wedge between her and Kimahri:
Kimahri: Kimahri not like Maester Seymour.Yuna: Aa! Shhh!¬Kimahri: Kimahri speak no more.
(Kimahri does not speak in her presence again for a very long time.)
(Tromell trying to lead Yuna away the INSTANT she arrives in Guadosalam!)
Not that she’s turned her back on her guardians completely, of course. But she’s keeping them out. She’s “too quiet.” She won’t confide in Lulu. She runs away from Tidus in the Thunder Plains Inn. She can’t tell her guardians what’s on her mind until she’s talked to Seymour about it first:
Yuna: For Spira’s future…and Yevon’s unity. I thought it would be the best thing to do.
Wakka: Yuna, just one question. Can’t you just talk to Maester Seymour? You’ve got to marry him?Yuna: I don’t know. But I think it is the right thing to do.
Yuna is really, really mixed up. On the one hand, she’s half bought into Seymour’s B.S. about taking him as her Lord Zaon, “for Spira’s future.” On the other hand, his murder of his father is a threat to “Yevon’s unity”:
Yuna: I wanted to confront Maester Seymour about his father, Lord Jyscal. I wanted to convince him to turn himself into Yevon’s judgement.Lulu: In exchange for marriage?Yuna: Yes, if that’s what it took.
She’s torn between following Jyscal’s final request to “stop my son” or Seymour’s insistence that she marry him and bring hope to the people of Spira. Somehow, she’s trying to do both.
Either way, she is just not focusing on what this means for her guardians. Look at the following exchange, in which it’s Tromell, not Yuna, dictating where they’ll go. She can only stammer, apparently at a loss about what to tell them, what they should do, what's going to happen to them, or even when she’ll be able to talk to them again:
Yuna: I want to keep journeying, even if I marry. Do you think that Maester Seymour would let me?Tromell: But of course, my lady. Lord Seymour wishes nothing else, I’m sure.Yuna: (Smiles and bows head to guardians) Goodbye.Tromell: Well… We must follow Guado tradition. (to guardians) I’ll have to ask you wait here a little while longer. I’ll send someone to escort you. (Leaves)Yuna: (Hangs back) I…Auron: We’re all with you. Do as you will.Yuna: Thank you. (Leaves)
She is no longer with them. Seymour played her like a puppet.
This isn’t to dump on Yuna. Auron’s right: “Make mistakes. That’s what youth is for, after all.”
She learns from her mistakes and is soon standing up to the maesters and casting off the entire Church of Yevon when it gets in the way of her pilgrimage, just as Auron had urged. But that was not an easy thing to do. It makes her crisis of faith and her character growth far more compelling than if she’d blithely blown off the church and the maesters like Tidus did, right from the start.