She wasn't angry with them because she didn't WANT to be the saintess. She's happy being a researcher. And as far as the crown prince goes, he's a self centered ass, and he got what he deserved from his father publicly humiliating him then taking away his athority and placing him under house arrest. What could her being angry at his stupidity have possibly done more than what the king did? The King was hoping his son would correct his stupidity, but when he didn't the king stepped in and did it for him. Why bother getting angry over someone that is not of your concern, right? As soon as she became part of the research development department she forgot about anything but having fun every day. Why ruin that by being pissed off at some idiots that can't even touch you anyway? That seems more foolish to me. I don't think she's a pushover, she simply doesn't see the point in letting others actions ruin the joy she is having. We should all learn to do that.
It kinda getting boring after Sei always follows the flow and not angry at royalty like dafuq she should getting angry because royalty ignore her more than 2-3 month she get summoned but she so submissive and you know saint to forgive everyone she near to getting title as Jesus tho... if all isekai people like this how easy people from 21 centuries get foolヾ(☆▽☆)