Shorts are just not acceptable on adults in any city outside of the US. You can get away with them at beach resorts maybe, but not in the city. I wear loose washable silk or cotton dresses - which are a lot cooler than shorts - or capri pants. If you are going to any religious sites (this includes Recoleta Cemetary or other cemetaries) it can be considered disrespectful to wear shorter skirts than knee length.