Why do I need a driver's license or state ID for Apple Cash verification when my sister didn't?

Here are the requirements for Apple Cash:

• Be at least 18 years old and live in the United States.
• A compatible device with the latest iOS, iPadOS, watchOS, or visionOS.
• Two-factor authentication set up for your Apple Account. 
• Be signed in to iCloud with the same Apple Account on any device you want to use to send or receive money.

Set up Apple Cash - Apple Support

After you reach a certain threshold of aggregate transactions, you will be required to verify your identification. This is a Government regulation placed on all banks and is called the Know Your Customer (KYC) laws. These were enacted with the US Patriots Act along with the Bank Secrecy Act. Apple will not be able to help you with this as they are not a bank and the verification requirements with Apple Cash is for GreenDot Bank, which is the bank that administers Apple Cash. More about the verification process is available here.

Verify your identity for Apple Card or Apple Cash - Apple Support