I'm with dkelly... that epicurious cake is delicious. I use Ghirardelli cocoa... I prefer it to hershey's, but that's my palate. I don't like some higher end chocolates either (Callebaut is one that comes to mind). Using hershey's won't result in an awful tasting cake though so if that is your love... then by all means use it.
I'm thinking that if she's complaining and no one else is... it's about the money. And she liked the free cake to boot? Were they 100% the same? Fillings and all? If so... then I say there is no merit to her complaint. Does she know that both cakes came from the same exact batter? I'd let her know that.