If it were me I would not punish her for hiding the note.
Did you ask her why she felt the need to hide the note from you? Did you question her viewpoint regarding the "disrespect" that was supposedly done?
I'd keep in mind that we live in a society where it is okay to disrespect children right and left while at the same time DEMANDING that these same children 'show' respect for the adults.
Also, a lot of what children do that is considered disrespect is actually them...