sent money on Apple Pay last night and it still says pending on the receivers end

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/

Does your account or your sister’s Apple Cash account have any restrictions in place?