After submitting DS-160, your fiancee will get a DS-160 confirmation with barcode. She needs that, so make sure to follow the instructions for printing it out. But the DS-160 confirmation is different from the MRV receipt.
To pay the MRV fee, generate and print a deposit slip using -- https://www.ustraveldocs.com/ph/pmisdepositslip.htm?amount=265&country=philippines
Follow the instructions for payment at RCBC. After paying the fee, the bank will issue a receipt. Wait 1 business day after paying, then book the interview appointment using the receipt number from the bank.