I tend to get Aspects out of the stages of the back grounds.
So
Back ground
She grew up a normal girl
Aspect "Girl next door"
Rising Conflict
but not long ago her grandma died and told her on the deathbed about her familys secret:
Her family are a kind of guardians which guard the border between the Otherworld and our world against intrusions from the other side. She now inherits that duty.
Aspect: Guardian of the borderlands
First Story
I imagine her as a kind of monster hunter, trying to life a normal life while trying to fight the monsters which strangely start to cross the border in greater numbers then ever before because of some impending cataclysm or such.
So a good First story would be first time she had to take down a monster and how that effected her life
Aspect:Monster hunting wrecks your social life
Guest Star & Guess Star redux you need to have the other P.C.'s stories so you can see how you will interact with their first stories.
Then the two aspects from those events will come out of that - so they could be anything.