The Princess's Spirit actually defies precise definition. Novels like TaraElla's 'The Princess's Spirit' trilogy illustrate what it is. But here are several ground rules:
1) Belief in one self's ability to make things right in the end
2) Never giving in despite the odds being against you
3) Being proud of your sense of style, even if others don't like it
4) Never change who you are, even if others bully you for it
5) Loving life, and loving the people around you
6) Helping those less fortunate around you. Sometimes this requires courage too.
You can further understand the TaraElla approach to the Princess's Spirit by reading the novels.
The Princess's Spirit Trilogy #1-3: An Early 21st Century Liberty Movement Story