Most doll manufacturers readily disclose that ink doesn't come off vinyl. Would a print-out e-mail from American Girl suffice? It's definitely at worth writing them and asking them and seeing if they will help you this way.

My Life of Faith doll came with a warning not to get ink on her. Hopefully AG would also be open about this.

PayPal is supposedly tough to deal with in asking for a refund, so stick to your guns and don't back down!