If your friend used her Paypal account on Amazon, she couldn't do it directly, she must have used a work-around. See www.businessinsider.com/how-to-use-paypal-on-amazon-cards-2019-2?r=US&IR=T
"There are two major reasons that Amazon does not work with PayPal. First, historically PayPal was a part of eBay, one of Amazon's direct competitors. From 2002 into 2015, PayPal and eBay were linked together. PayPal has since split into an independent brand, but their partnership with eBay remains strong.
Second, PayPal is a direct competitor to Amazon's own payment service, the rather bluntly named Amazon Pay. Just as with PayPal, Amazon Pay is accepted by numerous third party retailers, letting you use Amazon payment methods beyond the immediate orbit of Amazon itself.
Perhaps she meant Ebay?