Viviana,
I am not aware of a way to get the shapefile data into a FlexViewer app without publishing it as a service (other than the shapefiles widget, but that doesn't give you popup access to the attributes, just displays and a single label).
I believe the ArcGIS Online account can be used for this ( http://www.arcgis.com/about/features.html ), but I have no experience using it at all.
I see that they offer a 30 day free trial, maybe this will work for you.
Otherwise, maybe someone else with more insight will reply to this post,
R_