Cierra and “The Envelope”

 Why would Cierra give a flying fig about the envelope?  She’s how old, 10?   Why would she be so interested in keeping it for her Dad?  I guess she’s supposed to be acting like "little detective" like her Daddy.  Obviously she knows what a person looks like when they are for hire and money passes hands.  She doesn’t know either person in the photo, until Kristen was at the table with table.  This envelope story keeps getting dumber and dumber.