There is no frustration. Her father already heard the news and she is already departing, with or without his blessing. She is only trying to tenderly explain it to him in a way he might understand and respect. There is no hint of anger or frustration, just a bit of melancholy that she is leaving her town possibly without her father ever understanding her actions and it is her last chance to articulate to him why she has to leave. It's my favorite number in the show.
"What can you expect from a bunch of seitan worshippers?" - Reginald Tresilian