Very interesting post card! This is an early valid usage, because on July 1, 1913 parcel post stamps became valid for all purposes for which ordinary stamps were valid.
It looks like it has a Chilton, Wisconsin RPO (Rural Post Office) cancel. Apparently Miss Esther Stiedl had moved to Milwaukee. The card was routed from Chilton to Appleton, Wisconsin where it received the straight line cancel and then sent on to Milwaukee.