To be honest I don't have like a super planned theme for her. Most things in her story are just the events that have been happening because of her decisions and disposition.

But I guess one important aspect that is tackled in her story and is one of the central themes is accepting that no one has their life figured out. Even adults, people who seem successful in their career, are in constant doubt as they're not all-knowing. And Briar's story is also a story of grieving and getting closure.

Another theme going on is 'time'. While some characters in her story are too fixated in the future, some others, like Briar, are stuck in the past and can't look forward. Her story is also one of accepting and embracing the present, without forgetting where she came from and keeping the future in mind.