Refund on apple cash

She has 7 days to setup her account and then it is automatically reversed (refunded). If you want it sooner, please contact an Apple Cash Specialist at Green Dot Bank. Apple Cash is a service that’s administered by Green Dot Bank. Contact an Apple Cash Specialist at Green Dot Bank by calling (877)-233-8552 or by calling 1-800-MY-APPLE

https://applecash.greendot.com/termsconditions/

Your friend will have 7 days to receive the money. If after that time it has not been accepted, then it will automatically be returned to you in 1 to 5 days after that.

Also if it has not been received, you can tap the transactions when viewing the Cash Card and will have an option to Cancel the payment. Not sure if that applies if the Cash card has not been set up though. For more information:

Send and receive money with Apple Cash - Apple Support