It's white or yellow corn flower used for making arepas, bollo, etc. I've seen it all over Colombia, but I've never seen it here. Hell, if you want arepas here you have to go to the few restaurants that have them (like this place: http://www.guiaoleo.com.ar/restaurantes/Arepera-Buenos-Aires-9802), or get them delivered from someone. I just asked my husband if he could remember anything about the arepa delivery lady we ordered from a couple times a few years ago, but he can't.
Search "arepas Buenos Aires" on Facebook, and you will find some pages like this: https://www.facebook.com/arepas.comeme?fref=ts
Maybe one of those delivery services could help her out?