On the suspected time jump and change in attitude:
Seriously. At this point she’s walking in to the Great Tree at ease with blue child walking with her, complaining at it in an exasperated way yes but almost in the way she bickered at Eugene. (And why not, it has been her only company for MONTHS, it first came to her wanting to be her ‘friend’, at this point in time she has almost started treating it like one.) This is way different than last we saw on the day with the red spikes. At this point she is perfectly willing to go for the scroll in Corona whereas on that day, she was still terrified, though the episode did end with her resolving to do SOMETHING.
Her confrontation with her father definitely happened between that day and this one. She’s slowly making her way back but becomes aware that he is looking for her and trails him for a while in the labyrinth. This is one of the major fears we suspect is attached to going back to Corona — how can she face her father — and now here he is. He’s in a hostile location and knows something’s around, it might be Cassandra but even if it is he doesn’t know what to expect, so he draws his sword. Cassandra perceives that as a threat, she draws hers and goes on the attack, disarms him.
This is what she feared, her own father is coming after her, does not trust her. Did he ever even care for her in the first place? Obviously no one else did, why should she expect better of him? He’s demanding answers for her betrayal of her duty, it really is all about Rapunzel, isn’t it. He doesn’t care about her, he cares about the princess like everybody else.
Angry Cassandra is now yelling, she may have been blind to all this as a child but he KNEW these things, knew what he was doing, chose to do all these things which have hurt her so tremendously. Again, “you only did what was best for yourself”, he never cared about her. Why should she care about him, then? Why should she even fear him, fear what he thinks of her?
The line “THIS is MINE, THIS is MY destiny” comes after that, she’s yelling it at him but she’s also solidifying it for herself, she’s repeating it to really believe it. No one cares about her so she doesn’t have to fear disappointing them, she looks out only for herself now. She is in charge of her own happiness and she will seize that destiny which she believes will give it to her.
It’s ingrained in her, she’s so used to obeying her father, to showing she can follow orders as she pursued that dream of being a guard, that his command shakes her despite the wall of anger she has built around herself. But isn’t this just further proof? He’s not even acting like a father now, he’s trying to use orders to get what he wants, like always, she is done with that, she is done listening to other people.
She leaves that encounter even more resolved. What more does she have to fear from Corona now? She’s faced her father, she won that encounter, didn’t she? He proved that she shouldn’t even waste her time worrying about what people think about her because it’s not like they actually care, they’re just trying to get what they want. And if that’s all everyone else is doing, why shouldn’t she finally step up and take what she wants?