Apple Family Sharing

Please could you help with the following Apple Family Sharing problem:

1. We have set up Apple Family Sharing.
2. My daughter tries to buy a song on iTunes
3. Request to purchase comes to both parents
4. Either my wife (Organizer) or me (Parent/Guardian) approves the request
5. My daughter then gets a pop up 'Payment Verification Required' window which requires a password (see screenshot below).
6. What password must my daughter enter?

Any help would be appreciated.

Many thanks.