Are you in a neighborhood that participates in SAIL, which is Greenville's summer swim league? If not then know that some of the pools do allow non-residents to join. A SAIL team would be a great place for your daughter to make friends ... whether she is a 'good' swimmer or not isn't even all that important -- our team for example hosts all sorts of social activities outside of the pool to keep the teens interested. All the events are swum in time-determined heats so competition isn't lopsided and coaches emphasize personal time challenges rather than where you place in relation to other swimmers.
If she IS a good swimmer then SAIL is a low-key way to test the waters (haha) to determine if year-round swimming is a possibility for her. And if she becomes a year-rounder then she doesn't need friends anyway because swim team takes up all of your time
Website is swimsail.org