Sellers cannot charge buyers. Buyer has to approve and process the payment. If it is June, then it passed the PayPal claim period. Ask her for the transaction numbers, dates and each amount. You then could call PayPal for advice. Looks like this is an unexperienced buyer.
It happened to me once. A buyer claimed she was charged twice but I've only received one payment from her. I showed her a screen cap of my Paypal history of the month to prove I've only gotten one payment, and advised her to contact Paypal and her bank. THere is nothing you can do for her because you don't even have any info on the duplicated transaction.