all the ones on the cd's are really great S&W primers, if you don't already own them buy them and give them to her but I'd particularly recommend Kid Ebay, Andy from Lake Newbridge, the the two part audio guru call. they are all great at showing the weird slow build then sharp left turn that is the S&W trademark.
I second all the calls recommended so far, Mike beat me to Hammerhead, my all time favorite but here's few other favs you can get at the best show gems
1. Brock Peuchk, Neighborhood Hero - rivals Kid Ebay for going off on amazing tangents and completely forgetting its premise then circling back beautifully
2. Big Bill, Little Bill and Mr. Sherbert - the height of S&W surreal absurdity
3. RB calls about the Gathering of the Juggalos - what can I say, it's just amazing
4. Philly Boy Roys calls to talk about the world cup - I think this is a good one not only as a good PBR call but the presence of funny guests, Hodgeman and John Oliver being as bewildered by it all will make a newcomer feel less alone if they're confused
5. Darren from work shakes his money maker to that greasy funk - this is one of my all time favorite Darren calls