First, you will need to have the correct birthdate on her account. If not you are going to run into trouble when it comes to financial information with a false birthdate. This would likely lead to the account being locked and banks consider that fraud, and for the Apple Cash card, it is GreenDot bank that manages the account.
Update the birth date associated with your Apple Account - Apple Support
If you are unable to update the birth date, you will need to create a new Apple Account for your daughter with the correct birth date. For a child to use Apple Cash, they will have to be part of a Family Plan where you can then set up Apple Cash Family. The verification required will then be your identification.
Set up and use Apple Cash Family - Apple Support