I sent my daughter money from my Apple Pay to her Apple Pay and her Apple Pay is not working. How do I request that money back?

See the following from Send and receive money with Apple Pay - Apple Support

How to cancel or dispute a payment

1. Open the Messages app, then open the conversation and tap the payment. 
2. Your Apple Cash card will open in the Wallet app. Under Latest Transactions, tap the payment, then tap it again. 
3. Tap Cancel Payment.

If you don't see Cancel Payment, the person has already accepted the payment. Try asking the recipient to send the money back to you instead.

It can take 1-3 business days for the money to be refunded, depending on your bank or card issuer.