So, thanks to your suggestions, I solved the mystery. I'm ashamed I didn't think of this on my own, considering our technology enhanced/internet dependent era. Thank you, Mana, for suggesting to simply Google her name. I found that she sells "Drugs, Drug Proprietaries, and Druggists' Sundries"...wow, a drug dealer! I am certain it is her because the address listed online for the business matched the return address on the postcard. And, also like Mana suggested, we drove past her house (that was actually Paul's idea originally...no wonder you two are friends) and she lived in a nice neighborhood. I've decided not to call and I have put all our curiousity to a rest.
Also, thank you Carma for letting me know how she got my name and address.