Let me try to beak this down for you. Launch the Notes app on your iOS device and tap the button in the top left corner until you're on the Accounts page.
On the Accounts page you should have several options - This is where you choose the location that your Notes will be saved.
'On this iPhone' will save the Notes to the iPhone the Notes can only be deleted from that iPhone.
'iCloud' may be present if you have set iCloud to sync Notes so you can share them with other iOS devices -These Notes can be deleted from any iOS device set up to sync Notes with that iCloud account.
'Yahoo' or 'Gmail' (if you have both) will save the Notes to the email account - Here's the funny thing about saving Notes to the email account
If you delete a note from the iOS device it will stay in your email as that is where it was saved.
If you delete the note from the Email server via the Mail app of in Safari on the Mail providers site it also deletes the note from the iOS device. This would be like deleting a saved copy of any document on a computer.
My thought is your iOS device is set to save Notes to your Email account and you inadvertently deleted the notes from your device. I don't know for sure but good it's a good thing they where still saved to your email. For your friend I would have her check her email account for the missing notes. Hopefully she can recover them. Personally I would use 'On this iPhone' or 'iCloud' to save the Notes, the email option is to risky as I clean my Mail out on a regular.